I9EI H G7 THE EFFECT OF ATMOSPHERIC OXIDATION ON THE LUBRICATING PROPERTIES OF OILS JOHN BREWSTER HOFFMAN THESIS FOR THE DEGREE OF BACHELOR OF SCIENCE in CHEMISTRY COLLEGE OF LIBERAL ARTS AND SCIENCES UNIVERSITY OF ILLINOIS 1921 Digitized by the Internet Archive in 2015 https://archive.org/details/effectofatmospheOOhoff / 92 I H67 UNIVERSITY OF ILLINOIS ___J 2 ine._ 3 .Oj 192JL THIS IS TO CERTIFY THAT THE THESIS PREPARED UNDER MY SUPERVISION BY ENTITLED, _ John Brewster Hoffman effect of Atmospherio Oxidation on tho _ J02 P_§iliPi£ _ ?J: P-£ ejrtie s_ _o £_ _0 i_l IS APPROVED BY ME AS FULFILLING THIS PART OF THE REQUIREMENTS FOR THE DEGREE OF Approved : ^ : U v::^ _ . t Instructor in Charge O - <2- f . HEAD OF DEPARTMENT OF _ _ - / 500281 THE EFFECT OF ATMOSPHERIC OXIDATION ON THE LUBRICATING PHOPERTIES OF OILS. INTRODUCTION. It is a wall known fact that oils in use deteriorate in their lubricating power considerably, and it is the aim of this problem to determine how much of this is due to the affect of atmospheric oxidation, and what are the possibilities of nullifying this affect. A catalytic effect due to metallic particles in the oil may have some relation to the changes and also a method for reclaiming the oil may be suggested. To be truly valuable the effects of the exposure should be related to the lubricating power as determined by both the physical and chemical tests which have been found 'most effective for this purpose. The work on the oil should also imitate as nearly as possible the conditions affecting it in use; that is, the temperatures should be those commonly found in bearings, the light conditions should be those usually found in practice and the gas (air) should be used alone without studying the effects of sulfur dioxide, carbon dioxide, hydrocarbon gases, etc. as Conradson’haas suggested and devised his apparatus for. Finally, since we wish to approximate working conditions as closely as possible, the oil should be subjected to some mechanical treatment. Because of the fact that the lubricating problem is of great importance in industry, and because there is as yet neither a general knowledge of the causes of deterioration, nor a distinct idea of the changes taking place in the oil itself the problem has been undertaken. The work was carried out under the direction of Dr. W» S. Putnam, to whom I wish to express my thanks and appreciation for his * v ' ? ■ > i < v > . • ; /. ■ . ’ t ■ ■ ’ » a ■ * ‘ ? 2 very constructive criticism and helpful suggestions as to the way in which the problem should he attacked. HISTORICAL. Previous methods of studying this or similar effects on oils made use of 2 apparatus of the simplest type. C. E. Waters simply used erlenmeyer flasks, con- taining each about ten gms. of oil. These flasks were closed by filter paper (to exclude dust) and placed on white paper on a window ledge exposed to sunlight and air. Over four hundred hours of exposure was undergone, daily tests being made on the oils to determine the change in weight, loss of CO and H P 0. 2 ^ 3 4 galoziecki in 1891 and Hirsch 1894 tried the effect of blowing air through oil in the cold but found very little effect was produced except possibly 5 in the presence of sodium hydroxide. Arsinonann confirmed these results. In g 1892, Holde exposed samples of both mineral and vegetable oils to air and deter- mined the changes in acidity, unsaturation, viscosity and specific gravity. Ha found that mineral oils suffered practically no change compared to vegetable oils. 7 C. E. Waters in another series of experiments tried the effect of sim- ple heating in air. The carbonization or asphalt residue produced was the prin- cipal factor determined. These tests seemed to show that simple heating out of contact with air produced little residue. However, in his work previously refer- o red to, the oils which were exposed to air iTere also heated to 250 and the rela- tive carbonization noted, in these tests the carbonization according to waters' figures proceeded about 55 times as fast with heating, indicating that the effect producing the residue, probably polymerization, largely is due to heat to an even greater extent than to oxygen. Though the presence of the latter seems necessary, t V ' ■ i k , * . • 1 ,* ? • ' i , I I . • : § . i * ik, ' ■* « ' >• r 3 the majority of these previous investigations were conducted, by passing air or other gas over the surface of the oil. This doubtless produces similar results to the method of ’’blowing through” but relatively speaking the surface layer of the oil must be considered as over-oxidized with reference to the rest of the oil unless mechanical stirring was used. At a constant temperature there would be little in the way of convection currents, and practically the only diffusion of the surface layer throughout the body of the liquid, and the only means of pre- senting a new surface to the air would be by movement due to a difference in spe- cific gravity as oxidation progressed. A very slight motion might also occur through friction of the moving gas on the surface of the oil. The present problem tries to overcome these conditions, giving an action on the oil which more nearly approximates that found under working condi- tions. The tests, alsc^ are made with the prime object of relating the changes in the oil to its value as a lubricant, which practically none of the previous experiments attempted. APPARATUS. The apparatus used to oxidize the oil was constructed to heat the oil, blow air through it, and stir it vigorously at the same time. A tall beaker (C, see figure) holding 700 cc. of oil to be tested was placed in an oil bath (D) consisting of a larger beaker containing cotton seed oil. These rested on a ring stand and were heated by a blast lamp. A hollow vertical shaft (B) revolved by an electric motor and having two propellor shaped blades (p) at the lower end was placed in the test oil in the inner beaker, inside of the shaft a station- ary glass tube (A) was held. This tube extended to the bottom of the oil, where OXIDIZING APPARATUS CARBON RESIDUE APPARATUS 4 it was bant at right angles so that the stream of air blown through it would bub- ble through the oil. In order to make the conditions with regard to moisture and amount of air as uniform as possible the tube was connected to a side tube ex- tending to the bottom of a water column about a meter high. The water column reg- ulated the pressure, as long' as an excess of air was passed into the system, by permitting this excess to escape through the water, the pressure thus being con- stant and proportional to the height of the column. Just before passing into the oil the air was dried by inserting a CaCl^ tube in the line. The same oil was used throughout the tests, it being a standard auto- mobile lubricant of "medium” body from Pennsylvania crude. EXPERIMENTAL (METHOD) . Two test runs of 4 and 8 hours respectively at 60° were first made to determine the approximate amount of change which might be expected. Very little change was noted in the oil from these so the final runs were made as follows: Sample Number Time of Run Temperature Catalyst II 0 Room _ _ V 8 hours 97° - - VI 8 hours 196° - - VII 8 hours 147° - - VIII 8 hours 147° Fe The temperatures were maintained by hand regulation of the blast lamp and varied within three degrees during the ran, the temperatures given being the average for the 8 hours. sample VIII had a staging of five pieces of iron gauze within the inner beaker, with iron filings of about 30 to 40 mesh sprinkled on the gauze. Air was blown through this and stirring and heating conducted as usual. 5 After the oxidizing run the five oil samples were each tested for Flashpoint, Fire point. Carbon Residue, Viscosity, Specific Gravity, unsatura- tion, Capillary rise, Asphalt Residue, and Total Oxygen by combustion method. In all the tests made the relative rather than the absolute values were most desired. Flash and Fire were determined by the open cup method, Specific Gravity by hydrometer. Viscosity in seconds (two hundred cu. cm.) with an Engler. Capillary rise was determined by placing a thermometer stem open at each and in the oil and reading the rise on the thermometer scale. Only "soft ' 1 asphalt resi- dues were determined, these by precipitation in petroleum ether, filtration, solu- tion in benzene and subsequent evaporation in weighed dishes, unsaturation was determined by the method of Hubl 1 using a solution of 25 gm. of iodine and 30 gm. of mercuric chloride in 500 cc. of 95 $ alcohol, standardized against tenth normal sodium thiosulfate. After several hours digestion potassium iodide solution was added and the remaining iodine titrated using starch as an indicator. The results are expressed in cubic centimeters of iodine solution absorbed. For determination of carbon residue a modification of Conradson’s appa- ratus was used which was constructed as follows (see illustration). A large iron crucible about five inches in diameter was set into a hole in a piece of asbestos board about a foot in diameter, v/ithin the large crucible a smaller iron crucible was set on a layer of sand. Inside of the small iron crucible a porcelain cruci- ble to hold the oil was placed, covers were fitted to both of the iron crucibles and the whole apparatus heated by a blast lamp. A bunsen burner flame was direct- ed toward the edge of the outer crucible to ignite the vapors as they were given off. Heating was continued at a temperature just sufficient to produce inflam- mable vapors until no more vapors appeared. Then the flame was turned full on for five minutes. By careful regulation of the 6 rate of heating, checks on the deter- mination to within one -tenth of one percent were easily obtained. For ready EXPERIMENTAL ( MTA ) . conparison the extensive tables of results for the nine de- terminations on five samples of the oil will be tabulated, giving here only the average value for each determination, in all cases duplicate tests were made until the results checked within the limits of error of the determination. Sample Number Carbon Residue Oxygen Asphalt Residue $ $ % II .5(1) 34 .1(0) V .3(6) 47 .1(4) VI 1.8(1) 40 .6(9) VII .8(1) 5(?) .2(1) VIII .9(0) 63 .3(0) Sample Number Flash (C°) Fire (C°) Nhsatu ration ' II 213 241 c.c. of l 2 2.76 V 215 246 2.62 VI 217 247 2.51 VII 216 246 2.65 VIII 215 245 2.52 Sample Number Specific Gravity Capillary Rise Viscosity (sec. 60° C. ) II .863 69.8 196 V .663 68.3 199 VI .871 67.4 261 VII .866 69.0 221 VIII .867 67.7 225 s ' t k it*! t . ■ . 7 VISCOSITIES Sample II V VI Temperature Time Temperature Time Terape rature Time 21.3 1300 25.0 980 28.0 1420 28.0 765 31.0 700 36.0 895 39.5 455 36.0 537 44.0 520 42.0 405 40- 440 50.0 380 59.0 196 48- 308 56.0 297 66.0 163 56.0 225 63- 232 78.2 115 68.0 145 77- 147 80.3 110 75.0 130 88 115 84.0 105 86- 104 93.0 108 99.0 89 96- 92 104.0 93 99.5 87 106.0 83 120.0 75 VII VIII Temperature Time Taupe rature Time 28- 897 27.4 953 32- 730 33- 722 37.0 558 37- 590 43- 426 41.5 464 50- 319 47- 365 65.0 182 54.0 277 73.5 146 57.0 241 81 118 64- 194 91 97 72.0 152 100.0 88 81- 122 113.0 78 90- 105 100.0 93 , 1 * . f ♦ 1 s ' ■ i ' 1 8 EXPERIMENTAL (INTERPRETATION) Tlie results of the determinations are in general what one would ex- pect from the conditions of the run on the oil with the exception of Flash and Fire and possibly percent of oxygen. It is noticeable that the effect on nearly every property of the oil increases with the increase in temperature. The maximum change in every value except percent of oxygen has occurred in oil Number VI, run eight hours at 196° C. Next to this oil, VIII, run eight hours at 147° c. in the presence of iron particles, showed the greatest change. Then come in descending order according to magnitude of change, oils VII (eight hours 147° C.), V (eight hours 97° c.), II (fresh). Talcing up the determinations in the order in \diich they are here re- corded, one first considers Carbon Residue. This determination is relatively new in oil analysis and while its exact relation to lubricating power is not known, it would seem to be a valuable indication of the stability and homogeneity of the constituents of the oil. The work on the oil caused a great increase in the Car- bon Residue, and it is logical to assume that the lubricating power is corres- pondingly low. Asphalt residue shows a similar increase, and asphalt residues are not lubricants. The presence of the iron filings indicates that metallic particles in oil may catalyze the reaction in which it breaks down. Asphalt Residue was increased almost fifty percent due only to the iron, and Carbon Res- idue shows an increase in the same pair of samples which can only be due to the catalytic effect of the metal. The test for unsaturation is distinctly parallel to those for Carbon Residue and Asphalt Residue, particularly the latter. This is logical and con- 9 firmatory for the latter tests when one considers, as is usually done, that asphalt residues are the direct result of oxidation and polymerization of the un- saturated hydrocarbons in the oil. The most unaccountable and interesting deviation from the expected ef- fect occurs in the change in Plash and Fire temperatures. The variation in aver- age temperature between the different samples is but four degrees for Flash point and six for Fire. This is only a little more than the possible error in determi- nation by the method used. In the case of Sample VI, the oil was maintained at a temperature about fifteen degrees below its Flash point with a current of air passing through it, for eight hours, yet it lost, apparently, almost none of the volatile constituent which gave the observed flash. All during the run, however, vapors were visibly given off from the oil, and especially during the first two or three hours. It may be that the fifteen degree difference from the Flash Point was sufficient to protect the oil from loss of its volatile fraction, but i seems logical to advance another explanation for the appearance of the ''flash'’. This conclusion, from the observed behavior, is that ’’flash” and ’’fire” are not due to simple vaporization of the lightest constituents of the oil, but are due to cracking of the oil. If the first case were true the loss of vapors during the run on the oil should have made a much more noticeable difference in the Flash and Fire Points. Assuming the truth of the latter hypothesis, one immed- iately wonders if these tests (Flash and Fire) may not indicate something of more value than has been previously supposed. They would, it seems, indicate not only the temperature at which the oil begins to break down, but, what is more impor- tant, the relative stability of oils. The usual test might well be modified to consist of continued heating, when an increase in flash temperature would dis- 10 tinguish true volatilization of an oil mixture containing various fractions, from the cracking at constant temperature which would take place in a better oil of more uniform composition. In this way an accurate idea of the pureness and homogeneity of the oil might be obtained. The increase in Specific Gravity and Viscosity may be attributed to the same reactions of oxidation or polymerization or both which formed the as- phalt residue in the oil. This change in viscosity, while perfectly definite, was not very large. In special cases where an oil of very definite character should be used the change in lubricating characteristics due to its viscosity might be objectionable, but in ordinary use the variation is too slight to be noticeable, in internal combustion engines burning light liquid fuels there is almost always a mixing of the fuel with the oil which causes a decrease in vis- cosity counteracting the increase within the oil itself. The last test applied was decided on as a possible indication of that property of "oiliness", the simple ability to prevent friction between moving surfaces. It would seem that surface tension, the tendency of an oil to remain in contact with a surface should have some relation to the property. An oil of low surface tension would not maintain a film on the face of the bearing as well as an oil of high surface tension when subjected to the mechanical forces and the scraping effects in the bearing. The capillary tube used gave a rise of about four centimeters in thirty minutes. This time was chosen as being sufficient to permit the maximum rise with the tube used, for after that period of time no ob- servable change in height occurred in five minutes. With smaller tubes the rise and also the differences between samples were greater, but the effects of viscos- ity made a determination take several hours and the temperature and hence the vis is 2 ► » ’ • 1 * ■ ■ > V * ■ . : .. * : > v ■ « / 1 t 4 1 . ■ \ . t J- r - «>• . . ■ ■■ fi • i . i »• 1 - «# • * • 11 cosity would change before all the samples could be tested. Granting that sur- face tension is one indication of the oil's lubricating power, a definite loss is seen in the oil after use. CONCLUSION. From the above tests one may draw several conclusions, in the first place atmospheric oxidation has very little effect on a lubricating oil at temp- eratures below one hundred degrees, for Sample V showed only slight differences from the fresh oil. Using the same amounts of air though, an increase in heat of fifty degrees in samples VI and VII caused a marked change in the oil, and one concludes that the heating effects are very important. An oil would undoubtedly give much batter service if it could ba kept cool in use. The catalytic effect of metallic particles is vary noticeable, as the results on Samples VII and VIII show, in all probability oxidation effects would be influenced much more than other effects (as polymerization) by the metal, so one may conclude that the air in the oil plays a definite part in its change. Also because of the very notice- able effect of the metallic particles, a system in which the oil is used and re- used, returning to a reservoir after passing through the bearings, v/ould preserve the original properties of the oil much longer if a filter were installed to keep the liquid free of foreign material. * ■ IS , ' ■ - ' 1. ' 4 . * 1 ' t " . - 4 . . . . I > * 1 ■ ; , i > > . < . *20 !*fo 160 *8 o Temperature of Run 12 BIBLIOGEAPHY. 1. "Examination of Lubricating Oils", Stillman. 2. Bulletins 73 and 153, Bureau of Standards. 3. Zaits. Angew. Chem. (1891) pg. 416-419. 4. Cbem. Ztg. (1895) vol. 19, pg. 41. 5. J. Soc. Cham. Ind. (1895) vol. 14, pg. 282. 6. J. Soc. Cham. Ind. (1892) vol. 11, pg. 619. 7. Bulletin 160, Bureau of Standards.