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Sulfo-Acid Bodies in Lubricating Oils’ By G. L. Oliensis THE BARBERASPHALTC o . , MADISON, ILL.
NE of the most comstinate emulsions that baffle In “coking” lubricating oils in agitators, or in premature neutralplicated solubility his efforts. I n milder cases izing, some sulfo-acid bodies, etc.. are reincorporated into the oil from problems that the of emulsion, of course, he sludge. Breaking resultant emulsion or blowing bright merely causes oil chemist has on his hands could resort to agitation by some of these to go into perfect solution in oil. The Conradson is that involved in treating steam, or even by settling demulsibility test and the Vacuum steam test cause these bodies to petroleum oil with sulfuric a t slightly elevated temperbe thrown out as a soapy layer below the oil, and therefore constitute acid. Roughly speaking, atures, but in these more qualitatiue tests for these bodies, this soapy layer being sometimes the action of the sulfuric refractory emulsions such foamy, sometimes thick and homogeneous. The Vacuum Company treatment would be totally acid is a very simple oneregards as slop only the thick, soapy layer, but experiments indicate namely, it precipitates from inadequate. It has been the foamy layer to be slop in less concentrated form. the oil certain tarry and found, however, that the Evidence is cited that this layer consists of sulfo-acid bodies, gummy bodies which it renaddition of a small amount etc., and that the presence of slop indicajes imperfect treating. A ders insoluble in that meof a water-soluble soap and discussion as to whether or not its presence is harmful. and the agitation with steam will dium, and settles wit) these usefulness of the Conradson test in this connection follows. bodies to the bottom of often successfully break the the agitators in the form most persistent emulsions; of sludge, which is then drawn off, leaving the oil free of all and it is significant that a water-soluble soap rather than impurities. Actually, however, the action of sulfuric acid an oil-soluble ingredient has to be used, because it indiis far more complicated and far less clear-cut, and the pos- cates that the bodies responsible for the obstinate emulsions sibilities of intersolubility among the many reaction bodies in those cases must have been essentially of the opposite oil-soluble emulsifying agents, such as formed are well-nigh infinite, as will be observed from the type-namely, following brief summary of the more important of the many neutralized sludge bodies. reactions involved: After an emulsion has thus been broken, the oil is by no means entirely free of the hydrocarbon bodies that were 1-The diolefins and similar unstable hydrocarbons in petroleum oil are, generally speaking, carried down by the sulfuric first responsible for it. The oil still shows a more or less pronounced haze, due to the presence of water which is held acid as an insoluble sludge. However, such portions of the sludge as remain in the oil, either through adherence to the agitator there in the water-in-oil phase by the emulsion-forming lining or through incomplete separation, are often in large part bodies still retained. T o get rid of this haze, the treater reincorporated into the oil in emulsified form during coking, usually blows the oil with air at a slightly elevated temperaand after neutralization become soluble therein, existing probture. The function of this blowing is purely mechanical; ably as oil-soluble colloids, which recent investigations have indicated are so favorable to emulsions of the water-in-oil type. it helps carry the water globules out of the oil in the jet of 2-The mono-olefins and aromatic hydrocarbons, when treated air, and it would be possible to render an oil bright by merely with concentrated sulfuric acid, form with the latter very com- heating it a t some temperature below the boiling point of plicated and generally unstable alkyl sulfuric acids and esters water till the moisture has volatilized; but the emulsionof that acid, many of which are soluble in the upper oil layer and forming bodies are not removed a t the same time, and have remain there, whereas a portion is soluble in the acid sludge and is carried down into the latter. These bodies, during coking and only entered into genuine solution, or colloidal solution, subsequent neutralization, are probably modified considerably through the dehydration process involved in blowing the in their solubility tendencies; but it is safe t o assume that a t least a large portion of them is retained in the oil to the end, oil bright. These foreign bodies exist in very small amounts in the in the form of more or less unstable neutral esters of sulfuric acid and alkyl sulfates which may be soluble both in oil and in water. finished oil, and it is therefore practically impossible by chem3-Aromatic and other hydrocarbons, in presence of fuming ical tests to identify them accurately in their manifold maniacid, form ( a ) sulfonic acids, which after neutralization are festations. Fortunately, however, advantage can be taken converted into water-soluble sulfonates, and ( b ) the so-called of an interesting reaction which takes place when such an oil naphthenic acids, which are soluble in oil in their acid state, and is agitated with steam in the presence of water and then alin water when neutralized to naphthenates. These sulfonates and naphthenates are genuine water-soluble soaps of unique lowed to settle. The steam seems to bring down these colproperties, though their bearing here will be limited to their loidal emulsion-forming bodies in the form of either a creamy tendency to form oil-in-water emulsions. or foam-like layer which collects between the oil layer above It will thus be seen that by the time it has been coked and and the water layer beneath. The usefulness of this reaction has been recognized in two neutralized, the oil, so far from being clear of all unsaturated and tarry bodies, may contain a formidable collection of all current demulsibility tests, developed, as far as we know, kinds of oil-soluble and water-soluble colloids, soaps, and other independently of one another. One is known as the “Vacuum compounds, much of which, being of a nature calculated to Steam Test,” and the other as the “Conradson Demulsidevelop oil-in-water and water-in-oil emulsions, helps to bility Test,” which is fully described in past literature. reincorporate into the oil any sludge bodies present in meVACUUM STEAM TEST chanical suspension, and thus still further aggravates the emulsion-forming properties of the oil, as described under (1) The Vacuum steam test is rather crude. It consists of above. The result iF that when the treater has reached the stage of placing about 2 in. of water in a pint or quart milk bottle, washing the neutralized oil, he is often confronted by ob- adding 1 in. or so of oil and agitating with open steam. The mixture is then allowed to stand aside for about one-half 1 Presented before t h e Division of Petroleum Chemistry a t t h e 64th hour and the appearance of the emulsified layer, if any, beMeeting of the American Chemical Society, Pittsburgh, Pa., September 4 tween the oil and water noted. If there is no emulsified to 8, 1922
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layer or the layer is of a foamy, bubbly character, the oil is supposed to be of good quality. If, however, the emulsified layer is thick, creamy, and homogeneous in appearance, it is called “slop” (which is understood, in a general way, to be due to traces of sludge retained in the oil through inefficient treating) and the oil is adversely reported upon. The rapidity of separation of the layers is not especiallynoted. This steam test, though crude, is the only demulsibility test which judges quality by the appearance of the emulsified layer. CONRADSON TEST The Conradson test is far more precise in its provisions, but basically is the same. It consists in placing 100 cc. of the oil to be treated and 20 cc. of distilled water in a 200-cc. graduated cylinder and agitating with open steam for 10 min. The graduated cylinder is then placed in a water bath maintained a t 130’ F. and the respective appearance and volume of the oil, emulsion, and water layers are observed from time to time for 1 hr.; but the actual demulsibility figure is obtained, not from the speed of separation or the appearance of the three layers but from the percentage of water retained in the oil layer a t the end of the hour, the difference between 100 and the per cent of moisture giving the demulsibility figure. The Conradson method has not been used very much in the trade and is not very well known, nor has it yet received official recognition. The American Society for Testing Materials, which has been engaged recently in developing a demulsibility test, has made a rather keen thrust a t the Conradson test in its report, to the effect that there is no favorable comment to be found anywhere in current literature relative to the Conradson method except that of Mr. Conradson himself. The writer, however, after several years’ experimentation with the method, has found that i t is capable of precision, and can give concordant results repeatedly in the hands of different operators. I n fact, the generous amount of oil one begins with, and the comparatively large height occupied by the columns of oil, emulsion, and water in the cylinder, make it possible to take quicker and far more accurate readings than by any other method; moreover, the size of the receptacle, the proportion of water to oil, and the manipulation prescribed (which, by the way, is exceedingly simple) seem to bring out inter-reactions between the oil and water which in other emulsification tests (such as the Navy and the R. E. method of the A. S. T. M.) either fail to appear at all or are difficult to observe and measure; yet which, when present, can throw an interesting light on the quality and purity of the oil, quite apart from its demulsifying powers. T o bring out this twofold utility of the Conradson method, the test is conducted precisely as originally proposed by Conradson, but the method of reporting is modified as follows: ( a ) The volume of the three layers that separate out after emulsification is noted and recorded a t the end of each of the first 5 min., and a t the end of 10, 30, and 60 min. These data give very accurately the speed of demulsibility. ( b ) The appearance of the three layers is also noted, and will serve to indicate the quality and purity of the oil.
INTERPRETATION OF DATA OBTAINED DIFFERENCESIN TEXTURE OF THE EMULSIFIED LAYERThe Vacuum steam test bases its classification of oils upon the texture of the emulsified layer-a light, foam-like texture having no special significance and casting no reflection on the quality of the oil tested, while a thick, creamy, and homogeneous texture indicates poor refining. The Vacuum Company, therefore, seems to regard this difference in texture as a difference in kind. The author has found, however, that this
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differenceis not so much in kind as in degree, and that alight, foamy emulsion layer is caused by the presence in the oil of a much smaller amount of slop or emulsion-forming bodies than is found in oil yielding a heavy, creamy emulsified layer. This can be demonstrated in a number of ways: (a) b y introducing into an oil, A, of very rapid demulsibility and no emulsified layer, a small amount of oil, B, which yields a, pronounced slop; or ( b ) introducing into oil A a small amount of the isolated slop from oil B ; and then running a Conradson demulsibility test on such mixtures. If the slop were a definite compound that was thrown out of the oil by the steam, it could reasonably be expected that in the two experiments cited a n emulsified layer would be formed of the same creamy texture as oil B itself yielded, only in a volume proportionately smaller. Such, however, was not the case. The emulsified layer in the two mixtures came down light and foam-like in texture, growing denser and finer, o r lighter and more open, according as the amount of oil B in A was increased or diminished. Unfortunately, it cannot be assumed that the amount of emulsified layer is in all cases proportionate to the content of emulsion-forming bodies in an oil. This is because the rapidity of the breakdown of the bubbles formed during emulsification depends not only on the freedom of the oil from such bodies, such as soaps, oil-soluble colloids, etc., but also on the comparatively low viscosity of the material tested. Should the oil have a high viscosity, that feature would in itself retard the breakdown of the emulsion, even though entirely free of impurities. The question then arises-when an oil of comparatively high viscosity shows an emulsified layer, how can one decide whether it is due solely t o the increased body of the oil or to impurities present? This point can be settled either by diluting with a lighter viscosity oil of perfect demulsibility to a standard viscosity (and for that purpose 200 viscosity a t 100 suggests itself as most appropriate), or by repeating the demulsibility test on the same sample of oil. If the emulsified layer is due to emulsion-forming bodies present in the oil, these will be largely removed by the first steaming, and a second steaming of the same sample will show a marked reduction in the volume of the emulsion layer and in the time of separation; whereas if the layer is due merely to high viscosity, repeated steaming will not materially reduce the volume of the emulsified layer or the time of separation.
POSITION WITH RESPECT TO OIL AKD WATERLAYERS-SO far, we have been dealing with the appearance and volume of the emulsified layer. Still more interesting information is obtainable from its position with respect to the oil and water layers. -4s already indicated, the various impurities existing in a treated and finished oil may be roughly divided into two classes. The predominant and most frequently occurring class consists of bituminous colloids derived from the tarry matter in the sludge or otherwise, which are oil-soluble in nature; hence, tending to form water-in-oil emulsions in the presence of water. Besides these, the oil frequently contains traces of water-soluble bodies, such as soda soap, sodium sulfonates, etc., which tend to form, not water-in-oil, but oil-in-water, emulsions in the presence of water. According to whether the one or the other class of emulsifying agents is present or predominant in the oil, the latter yields, under the Conradson steam test, a differently “placed” or “built-up” emulsified layer. I n the presence of oil-soluble colloids there is a sharp line of demarcation between the upper surface of the emulsified layer and the oil above it, while the lower surface is wavy, uneven, and indefinite. The emulsified layer, furthermore, is densest a t its upper level and grows lighter and more open
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at its lower level, the whole layer appearing t o extend downward from the oil stratum into the water stratum. This kind of emulsion is of the water-in-oil phase, as is to be expected when the emulsifying agent is of the oil-soluble type. When water-soluble emulsifying agents are present, the exact reverse takes place. The sharp line of demarcation now appears between the lower surface of the emulsified layer and the water beneath it, while the upper surface is irregular and indefinite. Furthermore, the emulsified stratum is densest a t its lower level and grows more open in texture a t the upper, the entire emulsified stratum appearing t o extend upward from the water into the oil stratum. This kind of emulsion is of the oil-in-water phase, since it is produced by a water-soluble emulsifier. Oils containing such watersoluble soaps, even in exceedingly minute amounts, froth and lather excessively during steaming, and may even run over the rim of the cylinder if great care is not taken. In less frequent cases, where both classes of emulsifying agents are present, both the oil-in-water and water-in-o-il phases may be encountered in the same emulsified layer. In such cases there is no sharp line of demarcation between the emulsified layer and either the oil above or water below. Instead, it exists as a band which appears densest a t its center, and extends unevenly and with diminishing density both upward into the oil and downward into the water stratum. These phenomena may be conveniently demonstrated by incorporating into a perfect demulsibility oil small percentages of (a) neutralized sludge or calcium soaps, (b) water-soluble sodium soaps, or (e) combinations thereof, and studying the behavior of these mixtures under the Conradson demulsibility test. The steamed mixtures may even be allowed to cool and then shaken by hand, and as in that way the individual bubbles move more slowly and are of far larger size than under vigorous steaming, it is possible t o watch with the naked eye the gradual accretion of the mass of bubbles into an emulsified layer and its subsequent breakdown on standing; this is indeed an interesting and absorbing study, as it reveals more strikingly than anything else the essential difference in the behavior of an oil-in-water and a water-in-oil phase of emulsion, and makes it clear why the two, when building up between the oil and water strata, should assume the form they actually do, as described in the three preceding paragraphs. It can thus be seen that from the relative position of the emulsified layer can be deduced the character of the impurities present in the oil-particularly whether of an oil-soluble class, such as neutralized sludge and tar bodies, or of the water-soluble class, such as sodium soaps; and from the texture and density as well as volume of that layer, a roughly quantitative estimate may even be made of the amount of such impurities. Further work along these lines is now being done, which it is hoped will enable us to amplify the foregoing observations.
SIGNIFICANCE OF TEST The question now naturally arises-what is the real significance of all such information as this, as far as the actual quality of the oil is concerned? More specifically, i t j s contended that a demulsibility test would serve admirably in ascertaining the suitability of a turbine oil or a marine engine oil, as both of these oils are in continuous contact with steam or water; yet, the promptest separation is essential in the former while the most stable emulsification is desirable in the latter. But inasmuch as the greater part of lubricating oil production of present-day refineries consists of motor oil, which normally does not come in contact with water a t all, why worry about the
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demulsibility test? The appropriate answer to this question may be gathered from what has been submitted earlier in this paper-namely, that it is quite true the speed of demulsification is not a factor of primary importance in internalcombustion engines; but the demulsibility test also yields information having to do with the quality of the oil and its freedom from impurities, a matter evidently entirely apart from its demulsification tendency, and such additional information is of undoubted importance whether the oil normally comes in contact with water or not. But even so, it may be argued, inasmuch as the content of impurities, whether oil-soluble or water-soluble, is admittedly very small, how can we prove, even if these were deleterious to the oil in large amounts, that the small traces actually present could affect the oil to any noticeable extent? Finally, bearing in mind that many of the lubricants in high standing in the market are intentionally blended with fatty oils and soaps to impart certain desirable qualities to them, how can we tell but that these foreign ingredients revealed in the oil by the Conradson test do actually increase its lubricating value, efficiency, and durability? It is indeed difficult to answer these questions with assurance. However, even conceding for the sake of argument that the foreign bodies referred t o do benefit the oil, or are perfectly harmless, a chemist has a right to know, and the plant management should want to know, whether a particular oil has been carefully refined and cleaned, and the Conradson test will give him information on that point. However, who will say that these complex bodies under discussion do not hurt the oil? No one can deny that there has been considerable conjecturing in lubricating circles as to the causes of certain well-known breakdown phenomena in oils under service. Many hypotheses have been advanced to explain why some oils last so much longer than others, why some oils seem to deposit much carbon and others do not, and why, in fact, the production from the same refiner makes a brilliant service record one time and fails dismally the next. These hypotheses are gradually crystallizing into two distinct theories-namely, the “cracking’) theory and the (‘oxidation” theory. According to the former the oil is cracked by the exceedingly high temperatures to which it is subjected in the cylinders, and carbonizing sets in as a result. The “oxidization” theory is that actual cracking does not take place to any large extent, but that the oil, being a t all times in contact with the air, will, a t the moderately high temperatures to which the oil is exposed in service, oxidize to form tarry, insoluble bodies which eventually carbonize; and that the presence of sludge or other tarry impurities in the oil, or contact with the surfaces or dust of certain metal catalysts, will considerably aggravate this oxidization tendency. The writer is inclined to believe that there is a certain amount of truth in both theories, and that the disintegration of oil is due in part to cracking and in part to oxidation. When we bear in mind the tremendous heat generated a t the point of explosion in the combustion chamber, it is easy to see that cracking can undoubtedly take place through oil working past the piston rings into this cracking zone, and after partial carbonization dribbling back on the return stroke to the main body of the oil. Furthermore, if this may be expected of a perfectly refined petroleum oil, cracking of a much more aggravated form can be anticipated when the oil contains the notoriously unstable sulfuric esters and alkyl sulfates which are always formed when olefins are treated with sulfuric acid, and which tend to break up (even in storage a t atmospheric temperatures) into complex alcohols and sulfuric acid. This freeing of sulfuric acid from its esters is no doubt often responsible for a large portion of the acidity which develops in all lubricating oils on standing, and par-
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INDUSTRIAL AND ENGI,VEERI,YG CHEMISTRY
ticularly in service. And it is these decomposed and easily carbonized and corrosive bodies, among others, that would have t o stand scrutiny when we decide whether or not the impurities left over from the acid treatment are deleterious, and how they would affect the oil in actual service. Approaching this question from the angle of oxidization, we must bear in mind the powerful catalytic action exerted by the presence of so-called asphaltic bodies, in encouraging the oxidation of lubricating oils when subjected to moderately high temperatures in the presence of air, thus forming additional gummy, resinous, naphtha-insoluble bodies (as brought out so forcibly by the extensive researches of Mr. Waters of the Bureau of Standards). The close kinship between these asphaltic bodies and the colloidal bituminous bodies of the oil-soluble type derived from neutralized sludges that are discussed in this paper, as well as between the conditions of the oxidation tests conducted by Mr. Waters and those prevailing in the chassis of an automobile, is quite apparent. It seems clear, therefore, that when a substantial amount of such bodies exists in an oil, as will be revealed in the Conradson test, it may be expected that such an oil will oxidize arid gum up readily in service. From this discussion it would seem plausible that the elimination of all ingredients in mineral lubricating oils which tend
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to form any kind of emulsified layer, would a t the same time tend to cut down the possibility of either cracking or oxidization in the oil in service. It would no doubt be too radical a demand a t this time t o require that all oils be acid-treated with such nicety and precision (or that a less perfeot treatment be supplemented by such thorough filtering or alcohol purification) that the finished oil will show absolutely perfect demulsibility under the Conradson test, without any trace of emulsified layer; but a t least it seems pertinent to suggest t h e advisability of specifying that where an oil does yield an emulsified layer under that test, it shall be merely of a light, foamy character and not dense and homogeneous. This phase of the Conradson demulsibility test well merits further study, and while many other demulsibility tests have since been proposed, each of which has many points in its favor, none of the latter seem well adapted for the observation and study of the impurities thrown down by the steaming, as the Conradson method undoubtedly is; and whichever method is finally adopted for the determination of the speed of demulsibility proper, it is hoped the Conradson test will continue serving the chemist, as the criterion of cleanness and purity in oil.
T h e Examination of Low -Temperature Coal Tars-11' By Jerome J. Morgan and Roland P. Soule COLUMBIA UNIVERSITY, N E W YORK,N. Y.
T
HE specific methods for determining unsaturated ComPounds in the Presence of aromati C S may be divided into two classes :
centrated sulfuric acid, although thoroUghlY investigated for light hydrocarboW2Wasfound unreliable, especially for highly unsaturated Oils, and was unsuited to modification. A similar investigation has been made2 of a representative bromine-absorption method,3 but this was unsatisfactory on ~ c c o u n tof substitution4 as well as addition reactions. For this reason the use of the bromine number, even when compensated for substitution reactions, is less desirable than the iodine number. IODINE KURIBER-A Hanus iodine solution was Dremred and used according to standard procedure in the determination of the iodine numbers of low-temperature hydrocarbons after various treatments. The erratic and nonconcordant results obtained prompted an investigation of this method, with the purpose of so standardizing the conditions that consistent data could be secured. The principal factors of consequence were found to be: (1) the ratio of bromine to iodine in the Hanus solution, ( 2 ) the weight of sample used, and ( 3 ) the time of reaction. The effect of a change of the bromine-iodine ratio under similar experimental conditions upon a hydrocarbon sample
I n a previous instalment of this paper the examination of phenols from low-temperature coal tar has been treated, and a procedure given for separating the hydrocarbons into a portion containing paraflns and naphthenes and another portion containing Unsaturated and aromatic compounds. The method for estimating the proportions of constituents in thefirst portion has been discussed. The present section deals with the separation of aromatic and unsaturated compounds from a mixture. The methodfinally adopted, after studying uarious unsuccessful methods of determining each in the presence of the other, as well as the actions of aluminium chloride, sulfuric acid, and mercuric acetate. was extraction by liquid sulfur dioxide, which, when carefully controlled, yielded a fairly pure fraction of unsaturated hydrocarbons on account of the absence of the more than traces of aromatics in the low-temperature tars.
I-Methods indicating relative saturation, by determination of: (1) Maumene number (2) Bromine number (3) Iodine number II-Methods depending on the actual removal of unsaturated hydrocarbons by : (1) Aluminium or zinc chloride (2) Siilfuric acid of various concentrations (3) Mercuric acetate
None of these methods was considered satisfactory as giving accurate data on the percentages of unsaturated hydrocarbons in the mixture in question, but sufficient interest attaches to the investigations to warrant their review here.
MXTHODS INDICATING RELATIVE UKSATURATION These methods were investigated with a view to finding a measure of efficiency of separation, since the reduction of 1 per cent potassium permanganate solution proved too delicate to indicate the reduction of unsaturation in the successive steps. The Maumene number, a measure of the temperature rise of a mixture of the oil in question with con-
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Dean and Hill, Bur. Mines, Tech. Papev 181 (1917). McIlhiney, J. Am. Chem. Soc., 2 1 (1899), 1084. 4 Fischer and Gluud, Ges. Abhandl. Kennfnis Kohle, 2 (1917), 315, experienced difficulties from substitution reactions in the use of t h e bromine number as a test of the degree of refining of low-temperature benzines. 2
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Presented before the Section of Gas and Fuel Chemistry a t the 64th Meeting of the American Chemical Society, Pittsburgh, Pa., September 4 t o 8, 1922. Part I appeared in the June issue of THISJOURNAL. 1
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