INDUSTRIAL AND ENGINEERING CHEMISTRY
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in the opposite direction. When very weak acids are titrated, as in the case of a tan liquor, the falling off of the galvanometer deflections is very gradual and a t the end point a very slight movement in the opposite direction is caused by the addition of one drop of the alkali. The end point obtained, however, is very accurate, as the slightest motion of the galvanometer is easily detected by the eye, whereas the color change of the indicator that would result from the slightly decreased hydrogen-ion concentration could not be easily detected. Thus, when working with very weak acids, even in colorless solutions, the cadmium half cell is preferable and affords a more accurate method of titration than does the use of indicators.
gree of accuracy, as the personal equation has been eliminated. The slight movement of the galvanometer indicating the end point can be clearly seen by all, whereas the ability to detect very slight color changes varies greatly in different individuals.
Accuracy
YLISDER, transformer, and turbine oils in use form sludges that are oxidation products. The increasing consumption of lubricating oils and the decreasing supply of mineral oils emphasize the importance of conservation. The problem is being attacked from two angles-chemists are devising methods for cleaning used oils and they are studying the inhibition of oxidation. This paper deals with a particular sludge from oil (Sterling Quality Turbine Oil) used in a 25,000-kw. turbine of the Cleveland Electric Illuminating Company. The sludge, an emulsion of oil and water with adsorbed solids, lost most of the liquids by absorption in a few days when put on a porous plate; some on filter paper gave outside rings of water, which on drying left a blue coloration suggesting copper salts. Further examination showed that the sludge contained both organic and inorganic solids. The oil was removed by washing with petroleum ether, using the centrifuge. Three washings with 50 cc. a t a time were sufficient when a 3-gram sample was employed. Centrifuging the sludge alone caused a partial separation into two layers. However, in extraction with petroleum ether a better separation of the water was effected. Poking the mixture with a stirring rod helped along the operation. After the oil had been removed, the water could be squeezed out of wet sludge as out of a sponge. Determination of Water
The accuracy of the set-up was established by several different methods. Diluted solutions of acetic, lactic, butyric, and propionic acids containing two drops of phenolphthalein were titrated separately with 0.05 N sodium hydroxide. I n every case the same drop of alkali that caused the galvanometer to swing from the right to the left also caused the appearance of a faint pink color in the solution being titrated. I n the same way mixtures of these acids were titrated using phenolphthalein and phenol red as indicators, the galvanometer and indicator end points agreeing in each case. The method was further tested by titrating ten different tan liquors as follows: Ten cubic centimeters of the untreated liquor were diluted to 100 cc. and titrated by use of the cadmium half cell with 0.08955 N sodium hydroxide ad before. To IO-cc. portions of each of these tan liquors definite amounts of an 0.04535 N solution of mixed acids were added, diluted to 100 cc. and the titration by use of the cadmium half cell repeated with 0.08955 N sodium hydroxide. Phenol red was the indicator in the standardization of the acid and base used. The relationship between the number of cubic centimeters of acid added and the number of cubic centimeters of standard sodium hydroxide necessary to neutralize it is given in the table. 1
0.08955
N NaOH
I1
I11
0.04535 used in N acid 0 . 0 8 9 5 5 original added to N NaOH titration. used in 13 cc. No acid original final tiliquor tration added Liouor Cc. cc. cc. .~ 19.32 1 11.80 15 17.11 12.15 10 2 25 9.10 21.71 3 18.99 25 6.35 4 22.27 15 14.75 5 10 25.81 2 0 . SO 6 15 20.10 7 12.50 15 19.07 8 11.55 18.00 9 13.00 10 25.35 12.75 25 10
.
I V (111-1)
v
V I (V-11) Difference in 0.08955 NaOH volume N NaOH necessary of 0.04535 required for added N acid for added acid calcd. added acid to 0.04535 N and found c c. cc. cc. 14.85 -0.15 7.52 9.80 -0.20 4.96 24.90 -0.10 12.61 24.95 -0.05 12.64 14.85 -0.15 7.52 -0.10 5.01 9.90 -0.00 7.60 15.00 -0.15 7.52 14.85 5.00 9.85 -0.15 24.85 -0.15 12.60
From Column VI it is seen that very good results were obtained with this method, the errors in each case being very small compared with the differences of 0.5 to 0.8 cc. or more which are likely to result when the official method is used. Summary
A simple, accurate method for the determination of the acidity of a tan liquor, employing the cadmium half cell, has been presented. This method is well suited for a control method as it can be generally applied, is quite accurate, and can be used with a diluted solution of the untreated liquor; a colored or opaque solution offering no interference. This method is also easily used, the skill required for hydrogen-ion concentration determinations being unnecessary. It can also be handled by different analysts with the same de-
Examination of a Turbine Oil Sludge' By Albert Salathe RESEARCH LABORATORY, GENERAL ELECTRIC Co., SCHEKECTADY, N. Y.
C
Five to ten grams of the sample were weighed in a 100-cc. tube. The sample was washed three times with 50-cc. portions of petroleum ether, using the centrifuge. The washings were warmed in a tared beaker on the water bath in order to evaporate the petroleum ether; the residual oil was 46 per cent. The sludge was dried i n vacuo to constant weight, the tube resting in a beaker of warm water to hasten the operation. The loss in weight, 42.5 per cent, was attributed to water. Content of Water
Qualitative examination of the water from the sludge gave extremely interesting results. The blue rings on the filter paper were due to copper, for when an iron nail was put into some of the bluish green liquid, metallic copper in quantity resulted. The blue color of the water solution deepened on addition of ammonia. A considerable residue remained on evaporation of 1 cc. of water. Under the microscope crystals of calcium sulfate were identified. I n addition, calcium was found by the oxalate test and sulfate by the barium test. The water solution was very acid to litmus and had an acrid, metallic taste. Iron and zinc were absent. Iron was present in the oil-free &y sludge, but calcium sulfate was absent. Iron and copper soaps in turbine sludges are common. I n this particular sludge the acidity was due largely to sulfuric acid. Lower fatty acids and naphthenic 1 Presented before the joint meeting of the Virginia Academy of Science and the Virginia Section of the American Chemical Society, Lexington. Va., May 3, 1924. Received November 28, 1924.
April, 1925
I S D U S T R I A L A N D ENGINEERING CHEMISTRY
acids were also present; acetic acid must also have been present, since acetaldehyde was, as is shown later. Saponification
It is well known2 that potassium compounds are more reactive than the corresponding sodium compounds; therefore, saponification with potassium hydroxide should be more effective than with sodium hydroxide. It is also well known that alcohol solutions are more effective in organic reactions than are aqueous solutions. Accordingly, the following experiment was tried: To a 20-gram sample of the sludge were added 50 cc. of 0.1 N alcoholic potassium hydroxide. This was heated on the steam bath for 3 hours in a covered Erlenmeyer. The alcohol was removed by evaporation and the oil was removed with petroleum ether. The resulting solution was filtered, and the clear, brown filtrate treated with hydrochloric acid in slight excess. The light brown “naphthenic acids” were caught in a Gooch crucible, dried, dissolved with absolute alcohol, and filtered. Upon evaporating the alcohol from the filtrate, there remained a dark brown, gummy mass of the “acids” weighing 0.108 gram. They were dry, resinous, practically odorless, and completely soluble in alcohol again. In such solution, A. J. Sherburne, of this laboratory, titrated them electrometrically, and found them equivalent to 9.63 mg. potassium hydroxide. Calculation gives C48H&OOH as the average composition of these acids. This is in line with Mabery’s3 conclusion that naphthenic acids of extremely high molecular weight occur in petroleum oils. For the purpose of getting quantities of the naphthenic acids for study, a series of saponifications was taied using stronger alkali. Fifteen grams of sludge were heated with 0.5 N alcoholic potassium hydroxide on steam bath over Sunday. After removal of the oil and alcohol in the manner described above, the lathery soaps were taken up with hot water, and titrated hot with 0.5 N hydrochloric acid, using phenolphthalein as outside indicator on spot plate. Saponification values equal to 52.5, 44.8. 50.3, and 53.7 mg. potassium hydroxide per gram of sample of sludge were obtained. To get the acid number, a 4.5-gram sample was mixed with 25 cc. of neutral 95 per cent alcohol, heated to boiling, and titrated hot with 0.05 N potassium hydroxide using phenolphthalein as outside indicator. As a result 10.7 mg. of potassium hydroxide per gram of sludge were obtained. Since this is only about one-fifth of the saponification value, most of the saponifiable part of the sludge apparently consists of soaps and possibly esters. Lassar-Cohn4 points out that prolonged refluxing with baryta water will saponify many esters and that limewater is similar but inferior because of its poorer solubility. It was thought by the writer that barium hydroxide would be less drastic in its action, less resinifying than potassium hydroxide, and that the soaps and acids obtained would be of better color. James6 states that lime soaps should be of good color and that lime will not resinify the aldehyde acids as will soda. With these points in mind, two saponifications were run, suspending powdered barium hydroxide octahydrate in 95 per cent alcohol, heating 2 hours on the steam bath, diluting with water, and titrating hot with 0.5 N hydrochloric acid and phenolphthalein as outside indicator. The acids liberated were of better color than when potassium hydroxide was used, and the results were about the same--namely, 47.1 and 49.2 mg. Lassar-Cohn, translated by Tingle, “Application of Some General Organic Reactions,” 1904. John Wiley & Sons, Inc. 8 THISJ O U R N A L , 15, 123.3 (1923). 4 Translated by Smith, “Manual of Organic Chemistry,” 1896, p. 354. The Macmillan Co. 8 Chem. M e t . Eng., 26, 210 (1922).
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The acids were prepared many times in connection with the saponifications. After titration the oil was removed with petroleum ether, the residue taken up with hot water, filtered, and the filtrate made acid with hydrochloric acid. The naphthenic acids were precipitated and were conveniently separated by centrifuging and then pouring off the supernatant liquid, which was always yellow. Since amyl alcohol was the only common solvent immiscible with water found to remove this color, it was concluded that the acids are slightly soluble in water. The acids were very soluble in methyl, ethyl, and amyl alcohols, in chloroform, pyridine, aniline, benzene, and slightly in ether. I n the dry state they are brown, hard, brittle, and resinous. These solubility data and the rule “like dissolves like” are in accord with the accepted ideas that these “acids” have alcohol, keto, aldehyde, and acid groups, and are rich in carbon. A few milligrams of the acids were treated with dilute sodium hydroxide; the acids were kept in excess, but the mixture was blue to litmus. Calcium chloride was added in slight excess to precipitate the calcium soaps and the aqueous supernatant liquid was neutral to litmus. The brown gelatinous precipitate was washed carefully to remove calcium chloride, sodium hydroxide, sodium chloride, and calcium hydroxide. The wash water gave no precipitate on addition of hydrochloric acid. Washing with 95 per cent alcohol three or four times gave some free acids. Iron soaps were made similarly, using ferric chloride and ferrous sulfate. The acids constituted 7.3 per cent of the sludge or 13.6 per cent on an oil-free basis. Determination of Acetaldehyde
RobinsonJ6reported the presence of acetaldehyde in mineral oil. Therefore, a few grams of sludge were shaken with 50 cc. of the oil and the whole was extracted with water. The water extract was tested qualitatively for acetaldehyde. It reduced ammoniacal silver solution and, on addition of sodium carbonate and powdered iodine, gave yellow crystals of iodoform. The “water” from the sludge was likewise examined for acetaldehyde. Two cubic centimeters of this “water” were placed in a 50-cc. flask and enough solid sodium carbonate was added to make slightly alkaline. A few crystals (powdered) of iodine were then shaken in and the flask was agitated, corked, and warmed; a fine yellow pulverulent mass was gradually thrown down. After an hour the mixture was shaken and the suspended iodoform poured from the excess of iodine. The liquid was centrifuged to separate the yellow crystals. These were recrystallized from ether. The leaflets were seen under the microscope to be iodoform. This was checked by recrystallizing known iodoform and examining under the microscope; the two sets of crystals were identical. It is evident that acetaldehyde can be estimated in oils and sludges in this way. Conclusions Although oxygen is determined in organic analysis only indirectly-that is, by difference-petroleum chemists believe that oxygen occurs in sludges from used lubricating and transformer oils. The work here reported indicates that oxidation has, indeed, been a cause in the sludging, for water and sulfuric acid were found in quantity; organic acidity is present, owing to aliphatic and naphthenic acids. A high saponification number shows the presence of acids, esters, and soaps. Acknowledgment The writer wishes to express appreciation to Charles Van Brunt for cooperation in the work reported here, which is a part of that done under his direction in 1923. 6
J . SOL Chrm I n d , 18, 232 (1899).
