INDUSTRIAL AND ENGINEERING CHEMISTRY
1240
tration. Also the tar-acid specification should refer to the fractions above 235" C. ( 5 ) Certain oil-tar distillates have a greater protective value against marine borers than that with which they have ordinarily been credited.
Vol. 19, No. 11
(6) Inorganic substances, by themselves, have little prospect of value in the preservation of marine piling against borer attack. (7) Chlorine treatment has no practical value in the protection of piling against marine borers.
Deterioration of Mineral Oils 11-Mechanism
of Oxidation and Action of Negative Catalysts as Determined by Static Methods'sz By Brian Mead and Collaborators
DEPARTMENT OF CHEMICAL ENGINEERING, MASSACHUSETTS INSTITUTE OR TECHNOLOGY, CAMBRIDGE, MASS.
I
N A previous paper on this subject3 results were shoxn of experiments, made by a dynamic method, to determine the mechanism of oxidation of mineral oils. This method of testing by bubbling oxygen through a heated sample of oil, while generally satisfactory when the oil sample oxidizes a t a relatively high rate, was used with difficulty when the experiment was of long duration or when a large number of samples were to be studied, because small differences in oxygen supply made large differences in the deterioration. I n one set of experiments oxygen was bubbled through several samples of oil by way of pieces of capillary tubing as nearly as possible of the same diameter. No concordance between the results was possible, however, on account of slight differences in internal diameter of the tubes. Another disadvantage of this method is that by the passage of the stream of oxygen through the oil some of the volatile products of the oxidation are removed from the system, and since these may have an appreciable influence on the progress of the reaction, their removal may c?use erroneous results. The mechanism of oxidation can also be determined by a static method, in either an open or a closed system. For the former, the method.consists in heating samples of oil in test tubes, the mouths of which are open to the air. By placing a batch of such tubes in an air oven maintained a t constant temperature it is possible to obtain fairly satisfactory and concordant results. However, in this case, too, only the effects produced by the oxidation can be measured, and not the amount of oxygen producing them. This method, or a modification of it, is the principle of the French and the Sligh oxidation tests. I n the Sligh test oxygen is substituted for air and the flasks in which the oxidation takes place are stoppered. A more satisfactory method seems to be to have the oil and oxygen in an enclosed space. As oxygen is absorbed by the oil, the amount so used can be determined directly by actual measurement. To determine the resulting change in the physical and chemical properties of the oil, it is necessary to discontinue the oxidation and analyze the oil. This method has one disadvantage-that it requires a separate apparatus for each determination. The apparatus can, hovever, be so constructed that it is necessary to disconnect only the part in which the oxidation takes place, using the remainder for the next run in the series. By having a num1 Combination of papers presented under the titles "Mechanism of Static Oxidation," "Prevention by the Use of Antioxidants," and "Mechanism of Static Deterioration of Transformer Oils," before the Division of Petroleum Chemistry at the 72nd Meeting of the American Chemical Society, Philadelphia, Pa., September 5 to 11, 1926. 2 The experimental work reported in this paper was carried out during 1924. 8 Haslam and Frolich, THIS JOURNAL, 19, 292 (1927).
ber of reaction vessels made up ahead of time, it is a comparatively simple matter to arrange the experiments so that they are practically continuous. Thus, for any given oil, if it is desired to determine oxygen absorption, acidity development, and sludge formation over a period of 20 days, it will be necessary to make twenty separate runs, the first lasting for one day, the second for two, and so on. It is possible by this method to get accurate oxygen absorption data for the whole period, and so to trace any unusual or unexpected trend in the reaction. The results reported in this paper were obtained by static methods, using both open and closed static systems. Part A includes the results from the closed static method, studying the effects of temperature, surface exposure, degree of unsaturation of the oil, acidity development, and sludge formation. Part B consists of a series of accelerated tests on S u j o l and a commercial transformer oil (No. 10 Transil Oil) by the open static method. Part C describes a study of the effect of various antioxidants on the sludge formation in transformer oils as determined by the open static method. PART A-STUDY OF OXIDATION B Y CLOSED STATIC METHOD By Brian Mead, A. C. Phelps, C. R. Washburn, a n d J . P. Warner
Experimental
One of the most difficult factors to decide upon and to control was the temperature of the reaction. Oils are rarely exposed t o temperatures greater than 90" to 100" C. in transformers. At this temperature, however, the oxidation is relatively slight, so that in order to get measurable amounts of the products of oxidation, or of oxygen absorption, it would be necessary to use a very large sample of oil. Many of the accelerated tests have been run a t temperatures as high as 150°, or even 200" C. At 200" C. there is not only conaiderable fire hazard from the sample being tested and from the heating bath, but difficulty is experienced in maintaining a heating bath. Even a t 150" C. both these factors are of importance. Accordingly, it was decided to operate a t a temperature of 130" C. The oil used for the heating bath was a cylinder stock of high flash and low free-carbon content. Bulb heaters were employed, since any type of open coil heatei gave such quantities of sludge that the bath could be operated for only very short periods. Efficient stirrers were installed, in order to maintain the temperature throughout the bath constant within 0.5" C. The heaters were so adjusted in value that the intermittent one, operated through a relay by a mercury thermostatic regulator, was in operation for the minimum amount of time. The apparatus is shown 'diagrammatically in Figure 1.
INDUSTRIAL AND ENGINEERING CHEMISTRY
November, 1927
I n the particular set-up employed it was possible to use five complete sets of absorption apparatus a t once. I n introducing samples of oil into the reaction bulbs, and in the subsequent manipulation, great care was taken to prevent splashing of the oil sample on the walls of the reaction bulb, as this would have upset surface relationships, the influence of which was to be determined. Results
On account of the pioneer nature of the work it was found necessary to attack the problem from various angles. It was manifestly impossible to follow any of them through to any final conclusion, or even to arrive a t a definite decision as to the influence of some of the variables studied. With reference to the type of reactions occurring in the deterioration of transformer oils, it was found that the rate of oxygen disappearance (Figure 2 ) was constant Tvhile the rates of acidity and sludge formation (Figure 3) were slow a t the start and became higher as the reaction proceeded. This result is in accord with the theory of intermediate stages of oxidation as set forth in the first paper of this series.3 The physical and chemical properties of the oils used in these tests are given in Table I. a n d Chemical Properties of Oils Used for Oxidation Experiments PROPERTY OIL 1 OIL 2 OIL 3 OIL 4 Average molecular weight, in 382 406 312 388 camphor hlillimols unsaturation per 1000 grams oil, determined by KI-KIO, 64.0 43.1 46.5 32.6 Millimols free acid, Der 1000 arams oil. deternined bv fitration ' with alcohol& 4.8 4.6 4.0 6.3 NaOH Millimols saponifiable per 1000 grams oil using NaOH 0 0 0 0 Saybolt viscosit;at 100' F. 189 303 77 108 Table I-Physical
It is now possible to proceed to a detailed discussion of the effects of the different rariables investigated TEMPERATURE-It has been pointed out thal, whereas oils in transformer service are rarely subjected to temperatures even as high as 90" or 100" C., in the tests used to determine their suitability as transformer oils they w-e heated in some cases as high as 200" C. It has been emphasized, in addition, that it is possible that a t such elevated temperatures there is a different mechanism in the deterioration from that a t lower temperatures. This difference was shown to exist by the following experiments: Equal samples of the same oil were placed in crystallizing dishes of the same diameter and heated to one of three different temperatures for the same length of time. At 130" and 140" C. sludge was formed, but none of it was insoluble in carbon disulfide. At 150" C., however, not only was a larger amount of sludge produced, but 37 per cent of it was insoluble in carbon disulfide. Very evidently, then, there is a change in the mechanism of sludge formation somewhere in the neighborhood of 140' C. This was additional support for the decision to operate a t a temperature not greater than 130" C. For the determination of the temperature coefficient of oxygen absorption, two sets of data are available (Figure 2)-one at 120" C. and the other a t 130" C. The oxygen absorbed per gram of oil over a period of 10 days at 120" C. is 5.9 cc., and a t 130" C., 14.2 cc. The ratio of these two quantities yields a value of 2.4 as the temperature coefficient, per 10" C., in this range of temperatures. It is satisfactory to obtain such a result since if the rate of diffusion of oxygen into the oil were the controlling factor, a much lower coefficient would have been obtained. As explained below: within the range studied (0.2 to 0.4 sq. cm. exposed to oxygen per gram of oil) the effect of surface exposed to oxygen per
1241
gram of oil a t 120' C. is less than the experimental error, while a t 130" C. the effect is more marked. SURFACEExposvRE-The second important variable is the ratio of surface of oil exposed to oxygen to volume of oil. I n none of the experiments was the oil sample agitated; in fact, special precautions were taken to insure that the surface of the oil remained quiescent during the oxidation. When the ratio of square centimeters exposed to oxygen per gram of oil was varied from 0.2 to 0.4 the same oxygen disappearance per gram of oil was noticed in a given time. There were slight variations due to unavoidable experimental errors, but the maximum and minimum rates of oxidation were both obtained when using 0.4 sq. em. of surface exposed to oxygen per gram of oil, This means simply that under the conditions of these experiments the rate of solution of oxygen in the oils was greater than the rate a t which oxygen was being used up in oxidizing the sample. These results are based on data obtained at 120" C. As the temperature is increased it is possible that the ratio of surface of oil exposed to oxygen to volume of oil might become a controlling factor in determining the rate of oxidation of the oil sample. With increased temperatures, not only will the rate of oxidation increase, but the solubility of oxygen in the oil will decrease. The rate of oxygen solution can be e x p e c t e d to increase with higher temperatures, however. The result will undoubtedly E= be that eventually a t e m p e r a t u r e will be reached a t which there is no longer an excess of oxygen in the oil over that required for the oxidation, and so the rate of diffusion of oxygen into the oil d l become controlling. It is perhaps worth noting that even a t 130' C. there is some tendency for the surface e x p o s u r e t o become c o n t r o l l i n g , while a t 150' C. the results indicate that this is un-Oxygen Absorption Apparatus Adoubtedly the case. mnecting condenser with reaction connecting reaction vessel with DEGREEOF UNSATU-BCption buret RATION OF OIL-Probnbe for flushing out apparatus ably the most impor- E-Side arm for filling apparatus with oxygen G-Gas-measuring buret tant of the other vari- K-Condenser, water-jacketed is the chemical L-Mercury-leveling bottle abies A--Graduated side arm to buret unsaturation of the oil $ ~ ~ $ ~ ; l ~ ~ ~ being used. It has long e s t o p c o c k been recognized in oil technology that to obtain a stable product the unsaturated content must be reduced as low as is consistent with economical practice. This is the main function of the acid treatment which is given to the oil subsequent to distillation. It is also the reason for the filtration process through which oils are put during refining. For the purposes of this article unsaturation is defined as the capacity of the oil for taking up iodine, since the iodideiodate method was used. Although this is somewhat unsatisfactory because of the possibility of substitution of iodine in the molecule,* it is thought t o be a reasonably accurate measurement for the oils used.
c
I
1
Johansen, THIS JouRN.44, 14, 288 (1922).
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I N D USTRId L A S D ESGIN EERl NG CHEMISTRY
I n the experiments herein reported, four different oils were used, with a variation in the degree of unsaturation from 54 to 32.6 millimols per 1000 grams of oil. Table I1 gives a comparison of the rate at which oxygen is absorbed by a sample of oil, with its unsaturation.
Vol. 19, No, 11
of 120" C. The method of operation was to expose a sample of oil to oxidation for a given time, obtaining the increments of oxygen absorption at intervals. If, for example, the acidity developed in 4 days was sought, the sample was exposed to oxygen for that length of time, the run being then discontinued. The acidity of the sample was then determined by direct titration, the sludge being evaluated a t the same time. The combined procedure was as follows: The contents of the reaction vessel were rinsed into a flask, using 60 cc. of alcohol to effect the transfer. The mixture was heated slowly to boiling, with vigorous stirring, and then poured into a separatory funnel, using further 10 cc. of alcohol in rinsing. After 15 minutes, during which time the mixture separated into two layers, the oil layer was drawn off for sludge determination. This consisted in diluting to twice its volume with petroleum ether, and pouring through a tared Gooch crucible operated under vacuum. The reaction bulb was rinsed with petroleum ether to remove any sludge adhering to the sides, these rinsings being also passed through the Gooch. The sludge in the crucible was washed free from oil, and heated to constant weight a t 100" C. 0 2 4 6 8 IO I2 For the determination of acidity, the alcohol layer from TIME IN DAYS the funnel was washed into a beaker, together with a further Figure 2-Relation between Oxygen Disappearance and Time 10 cc. of alcohol. T o the resulting solution was added a definite amount of standard alkali, and the excess back-tiTable 11-Comparison of Oxidizability and Unsaturation trated with standard acid, using phenolphthalein as indicator. (All figures on gram basis) The end point was liable to be somewhat indefinite on account (A) (B) (3 RELATIVE RATES UNSATURATION of the brownish color of the solution, but with practice reproOIL OF OXIDATION O F OIL (A) ducible and consistent results were obtainable. Cc. oxygen per MilZimoIs per gram oil 1000 grams The acidity thus determined is what might be called the 1 14.0 54.0 3.86 "free acidity," and does not include the acid in the sludge. 2 11.2 43.1 3.85 3 7.2 45.5 6.3 The acidity-time curve is shown as curve A in Figure 3. 4 4.4 32.6 7.4 If the last point on the curve is eliminated, the remainder From this table it is apparent that there is no strict propor- of the points can be satisfactorily represented by a straight tionality between the degree of unsaturation of the oil and line. If, however, the validity of the last point is assumed, its oxidizability, although the general trend of results is in then it is seen that there is here some evidence in support the same direction. Oils 1 and 2 were from the same base, of the theory that the reaction is autocatalytic. In other and were refined to approximately the same extent; the same words, it starts very slowly, proceeds a t an increasing rate was true of oils 3 and 4. The ratios of unsaturation to rate for some time, and eventually slows up again. If, as is done in curve A of Figure 4,the acidity developed of oxidation indicate a satisfactory constancy for each class of oil. is plotted against the corresponding amounts of oxwen absorbed-by the-oil sample, the &&e has 0 20 a distinct S shape. This can be interpreted as meaning that at first the oxygen absorption takes place more rapidly 016 11 than acidity is developed by the sample, but after a certain amount of oxygen ,2 absorption, acidity starts to develop a t an increasing rate, being catalyzed by the products of oxidation. and then 0 8 E eventually falls off again. It should be remembered that there are at least two products of oxidation, acidity and sludge, 0.4 and either of these may catalyze the formation of the other. SLUDGE FORMATIOX-The sludge was 0 4 I2 16 Bo determined by the method given in the CC.OXYGEN ABSORBED PER CRAM OIL TIME IN DAYS preceding section. Curve B in Figure Figure 3-Relation between: A-Acidity Figure &Relation between: A-Acidity 3 shows the amount Of sludge expressed Development and Time; B-sludge F ~ Development ~ ~ and ~ Oxygen . Absorption. ESludge Formation and.Oxygen Absorption t i o n and Time in terms of the tirne of exposure of the sample to oxygen, while curve B in Figure DEVELOPMENT OF ACIDITY-It has already been mentioned that one sign of the deterioration of transformer oils is acidity 4 shows sludge in terms of the oxygen absorption which accomdevelopment. A correlation of this acidity development panies its formation. It will a t once be apparent that sludge with the amount of oxygen absorbed by the oil and also with formation starts a t a very low rate and increases throughthe sludge formed during the same period has heretofore out the period of the tests. This may be considered as evinot been available. Oil l was used for this series of tests. dence for the autocatalytic nature of the reaction, although, The experiments were performed a t a uniform temperature as was pointed out in the discussion of acidity, the conten-
-
5
2
November. 1927
INDUSTRIAL AND ENGINEERING CHEMISTRY
tion6 that sludge formation is promoted by acidity has not been disproved by these experiments. It is possible, moreover, that soluble sludge is formed a t a constrtnt rate, but that by reason of acidity development it is either polymerized and so rendered insoluble, or that it was rendered insoluble by the acid in the mode of its formation. It would be of interest to determine sludge formation a t a definite controlled acidity, in order to settle this question. The experimental procedure in such a case would perhaps be difficult, but It would give v a l u a b l e information on the mechanism of oil deterioration. Finally, if comparison of sludge and acidity is made, the type of curye shown in Figure 5 is obtained. This gives some support to the theory p r o p o s e d ahove-that a c i d it y development promotes sludge forination. At first, acidity is develMILL!-EQUIVALENTS OF ACID oped fasterthan sludge Figure %Relation between Sludge a n d is formed, but very soon Acidity Developed the rate of sludge formation commences to increase, and so continues for the remainder of the experiment.
1243
PART E-STUDY OF OXIDATION B Y OPEN STATIC METHOD By Brian Mead, E. F. Dirks, a n d W. B. Bader
Experimental
The method of heating the samples was as given in Part A, the samples of oil being placed in test tubes in an oil bath which was itself in an air oven. All tests were performed a t the uniform temperature of 150" C. Two criteria of deterioration were used: ACIDITY DEVELOPMENT-The oil sample was transferred t o a beaker, using 60 cc. The sample was slowly heated to 60" C., with constant stirring, and was then allowed to cool to 50" C. It was then rapidly cooled to room temperature, and phenolphthalein added as indicator, together with an excess of standard alkali, the whole being stirred for 5 minutes. The excess of alkali was then back-titrated against standard acid. SLUDGE FORMATION-A4fter cooling, the oil was filtered through a Gooch crucible, and the sludge washed free of oil by means of petroleum ether.
In both cases duplicate samples were used, so that checks might be obtained. Results
Nujol was first used, in order that the method of experimentation might be developed and tested. The results for acidity development are given in Figure 6. It is seen that the acidity-time relation can be satisfactorily represented
Conclusion
1--Temperature markedly affects the rate of oxygen disappearance, the temperature coefficient being 2.4 per 10" c., between 120' and 130" C. 2-Over the comparatively small range of surfaces of oil investigated, 0.2 to 0.4 sq. em. of surface exposed t o oxygen per gram of oil, the amount of surface exposed has no measurable influence on the rate of oxygen disappearance a t 120" C. It is probable that a t higher temperatures the ratio clf surface exposed to volume of oil will become a controiling factor. 3-Both a t 1 2 0 " a n d 130' C., with mineral oils the rate of oxygen disappearance may be represented as a straight-line function of time. 4-Sludge formation and acidity development, both start very slowly, and their rate increases as the I!16 e x p e r i m e n t p r o gresses. It is possible that sliidge formaFigure 6-Relation between Acidity tion is catalyzed by Developed by Nujol a n d T i m e acidity development. 5-The rate of oxygen disappearance seems to be proportional to the degree of chemical unsaturation. For oil from .a given base this relation holds especially well. Funk, THISJOURNAL, 16, 1080 (1924).
b
4
8 I.? TIME IN DAYS
16
20
Figure 7-Acidity Developed by New Oil: AAcidity 0.12 Per Cent. B-After Standing in Laboratory for One M&th before Test, Acidity 0.15 Per Cent
by a straight line. No sludge was formed by this oil during the period of the test. The majority of the tests were performed on a sample of commercial transformer oil (No. 10 Transil Oil). There was available not only a new sample of the oil, but also one which had so deteriorated in use as to cause it to be discarded. The results obtained on acidity development are best shown by plots. Figure 7 shows the curve ( A ) obtained in a 10day run on the new oil. There is a marked S-shape to this curve. The same oil, when allowed to stand for 1 month in contact with air a t room temperature, gave a curve ( B ) , also shown in Figure 7 , in which the S-shape is much less marked. I n this period the original acidity of the oil calculated as oleic acid had changed from 0.12 per cent to 0.15 per cent. By mixing together new oil and varying amounts of the bad oil, the original acidity of the oil was adjusted to 0.14 per cent for a 2 per cent addition of bad oil, and to 0.20 per
INDUSTRIAL AND ENGINEERING CHEMISTRY
1244
Vol. 19, No. 11
cent for a 5 per cent addition. The curves for these two mixtures are given in Figure 8. On comparing the four curves (Figures 7 and 8) it is seen that with increasing initial acidity there is a marked tendency for the curve to flatten out. At the highest of these values for initial acidity, indeed, it becomes a straight line. This connection between initial acidity and acidity development is well shown in Figure 9. For an initial acidity of 0.12 per cent the curve is S-shaped, for 0.14 per cent it is convex upwards, and for 0.20 per cent it is sensibly straight. Sludge determinations yield a similar series of curves. Figure 10 shows the sludge developed by the good oil, and by the same oil after it had stood for a month in the laboratory exposed to air. Figure 10 also shows the effect of the addition of 2 per cent and of 5 per cent of bad oil on the amount of sludge formation. It will be seen that the influence of the bad oil is very marked in promoting sludge formation. TIME IN DAYS
Figure 9
Results
In Table I11 sludges are reported as per cent of a blank run made under identical conditions but with an oil containing no antioxidant. The figures give sludge as per cent of a blank run on the same oil under identical conditions, but containing no antioxidant. Only those giving the most marked effect are given in the table; other materials are grouped in the paragraphs below. The oils used for the tests were commercial transformer oils furnished through the courtesy of the Standard Oil Company of New Jersey.
Figure 8-Acidity Developed b y Oil Containing: A-2 Per Cent Bad Oil, Acidity 0.14 Per Cent; B5 Per Cent Bad Oil, Acidity 0.20 Per Cent
From this series of experiments it seems probable that sludge formation is catalyzed by acidity, either in the form of acid deliberately added to the oil or acid formed in the oil by the action of the oxygen upon it. These results confirm in a striking manner those reported in Part A.
Table 111-EBciency of Various Substances as Antioxidants in Preventing Deterioration of Transformer 0118 SUBSTANCE SLUDGE SUBSTANCE SLUDGE Pe7 cent Per cent Sulfur 18 Turpentine 56 Nitrocresol 18 n-Octyl alcohol 57 Xitrobenzene 19 Iodoform 58 Phenylhydrazine 40 Bases from crude anthracene 519 Tolidene (0.03 per cent) 52 Phenyl thiomethane 662 Cymol 55 n-Phenylene diamine 1240 Oils used, Humble and Eagle transformer oils Concentration of catalysts, 0.15 per cent Temperature of tests, 130' to 140' C. Time of test, 130 to 168 hours
Conclusion
1-The acidity development in commercial transformer oil is autocatalytic a t low initial acidity, but not a t relatively high initial acidities which are obtained by additions (up to 5 per cent) of deteriorated oil. 2-Sludge formation seems also to be greatly influenced by the initial acidity of the oil, much more sludge being formed a t high initial acidities (obtained by additions of deteriorated oil) than a t the low acidity of the new oil. OF DETERIORATION B Y USE OF ANTIOXIDANTS By Brian Mead a n d W. L. McCabe
PART C-PREVENTION
Experimental
The criterion of deterioration was sludge formation. X definite volume of the oil containing the antioxidant was placed in a test tube which was suspended in an oil bath, the bath itself being contained in an air oven a t the same temperature. The mouth of the test tube was open to the air of the oven. The sludge developed after about 130 hours' heating of the oil a t 130" C. was determined by filtration through a Gooch crucible and washing with petroleum ether until the filtrate was free from oil. The sludge was then dried to constant weight a t 110" C. in an air oven.
.I4 .li
6 V
.I(
8 K
+ .of i
23 2.04 0 Y)
4
5.04
.Oi
C
2
4
6
TIME IN DAYS
Figure 10
8
10
12
November, 192i
INDUSTRIAL AiYD ENGINEERING CHEMISTRY
The materials giving values above 60 are given in the following paragraphs: Between 60 a n d 75: Pseudo-cumol, menthol, furfural, hexalin, borneol, dekalin, iodobenzene, carbazole, pyromucic acid, diphenylhydrazine (0.75 per cent), trioxymethylene, dimethylaniline. Between 75 and 100: 9-dibromobenzene, diethylnitrosoamine, pine oil, camphor, hexamethylenetetramine, anethole, pyrogallol, oleic acid, fluorobenzene, dimethylglyoxime, tetralin, benzene azo-8-naphthol, oil blue, eucalyptol, acetone extract of crude rubber, glycocoll, phenetole, diphenyl, P-iodophenol, a-picoline, furoin, benzaldehyde, amyl fluoride, piperidine, hydrazine sulfate, oenanthol. Between 100 and 150: Erythrosin, geraniol, iodol, triaminophenol hydrochloride, safrol, nicotine, vanillin, triphenylmethane, aceto-toluide. citronella, P-dichlorobenzene, oil orange, succinimide, eugenol, p-iodoaniline, isoquinoline, sudan 111, diphenylamine, guaiacol, mesitylene, piperonal, diphenylhydrazine hydrochloride, 9-aminomethyl-m-cresol hydrochloride, pyridine, carvacrol, anthraquinone, p-anisidine, acetanilide, naphthalene, methyl-o-aminophenol 4- hydroquinone, methylphenylhydrazine, furfuramide, tin salt of m-aminodimethylaniline, spirit scarlet, anisole, lemon oil, p-aminoanthraquinone, ethyl hippurate, acetamide, dicyanodiamine, methyl a-naphthylamine, antipyrine, quinoline, oil yellow, trichloroquinone. Between 150 and 200: Oil savin, aminoisoquinoline, ethyl a-naphthylamine, cyclo hexane, asparagine, galactose, oil red, aniline, diethylamine, thiosemicarbazide, oxyquinoline, dibenzalhydrazine, eugenol methyl ether, oxamide, phenyl acetanilide, m-aminophenol, cresol methyl ether, lead oleate, rhodamine B, p-nitrophenol, urea, hydrazobenzene, p-toluidine, 8naphthol, phenylpyrazolone. Between 200 and 300: Cottonseed oil, 9-chlorotoluene, 0- and p-chlorotoluenes, casein, phenanthrene, acid fuchsin, diethyl selenide, allylphenyl thiocarbamide, aceto-p-phenylene diamine, m-diamidoazobenzene, dichloroquinone, eosin, a-naphthoquinone, aluminum hydroxide, tribenzylamine, n-butyramide, p-nitrotoluene, benzoquinone, benzeneazophenol, xylidine, a-naphthol, a-naphthylamine, brucine, oxanilide, benzothiazole disulfide, carhanilide, o-ditolyl thiourea, m-cresol, lead tetraphenyl. Between 300 and 400: Cyanine, benzaldoxime, hydrobenzamide, phenyl a-naphthylamine, 0-naphthylamine, phenols from crude anthracene, methylene iodide, diphenyl thiourea, indigo, hydroquinone, anthranilic acid, bromophthalimide, dioxy-p-methyl coumarin, dimethylaminoazobenzene.
1245
Between 400 a n d 500: Dimethyl ammonium dimethyl dithiocarbamate, 9-methyl aminophenol ‘sulfate, P-phenylene diamine, glucose, benzidine, phenanthraquinone, Bismark brown, dinitrophenol, p-aminophenol, pyrocatechol. 9-ditolyl thiourea, safranine, diamylamine hydrobromide.
Summary and Conclusion
Of the total number of substances used in these two tests, 177 in all, 48 have shown themselres capable of having an inhibitory action on sludge formation. The remainder have either comparatively little effect, or else accelerate the reaction, the majority being in the second category. Of those having the greatest inhibitory effect, there are three which stand alone: sulfur, nitrocresol, and nitrobenzene. It seems to be quite impossible to draw any generalized conclusions from the results, as to the types of compounds which act as antioxidants, since for every compound which acts as a negative catalyst one of the same type can readily be discovered which acts as a positive catalyst. The action seems to be specific, and not to follow any general rules by means of which the effect of any particular substance might be predicted. These results refer only to the definite stated conditions of experimentation, and their extension to other conditions is liable to lead to erroneous conclusions. Acknowledgment
Thanks are due the Tide Water Oil Company for samples used in Part A and for permission to publish some of the results, the Edison Illuminating Company of Boston for the samples used in Part B, and the Standard Oil Company of New Jersey for permission t o publish the results of Part C.
Clarification of Starch Conversion Liquors in Manufacture of Corn Sugar and Corn Sirup’ Improved Method By M. S. Badollet and H. S. Paine CARBOHYDRATE D I V I S I O N , BLlRfAU OF CHEMISTRY AND
I
N THE usus1 process for the manufacture of corn sirup
and corn sugar sodium carbonate is added to the acid starch conversion liquor to reduce the acidity and cause flocculation of some of the colloidal material. In a previous investigation2 the maximum flocculation of colloids in the acid “converter liquor” was obtained by regulating the addition of sodium carbonate until the isoelectric point was reached as determined by ultra-microscopic cataphoresis measurements. It was noticed that even a t the isoelectric point addition of sodium carbonate did not remove all the colloidal material and that after filtration the filtrate became turbid after standing for some time. Further observations showed that this turbidity occurred frequently, suggesting that clarification by the use of sodium carbonate done is relatively inefficient. An attempt was made, therefore, to devise a method whereby a greater proportion of the colloidal material in acid starch conversion liquors could be flocculated and eliminated. Theory A systematic study of a number of samples of starch conyersion liquors obtained from several manufacturers of corn 1 Presented before t h e joint session of the Divisions of Sugar Chemistry a n d Industrial a n d Engineering Chemistry a t the 73d Meeting of t h e .4merican Chemical Society, Richmond, Va., April 11 t o 16, 1927. * Paine and Badollet Facts Aboul S u g a r , 21, 1212 (19261
SOILS,
~ ~ A S H I N G T D. O Nc. ,
sugar and corn sirup revealed the fact that the colloid particles present in acid conversion liquors invariably carry a positive electric charge, whereas the colloids present in most sugar liquors, as well as in most aqueous suspensions, bear a negative charge. The positive charge is probably due to the unusually high hydrogen-ion concentration of the conversion liquor. When this acidity is reduced by addition of sodium carbonate this positive electric charge is reduced until the isoelectric point is reached, where the electric charge on the colloid particles is completely neutralized. This results in flocculation of a large part of the colloidal material but not necessarily all of it as shown by ultra-filtration tests. Since the colloid particles of the acid conversion liquor carry a positive electric charge, it was assumed that certain colloidal clays and earths, as well as other types of colloids which bear a negative charge a t the hydrogen-ion concentration of acid starch conversion liquors, would produce mutual colloid flocculation with the colloids of the conversion liquor and might thus cause greater colloid flocculation and elimination than sodium carbonate alone. Sodium carbonate would, of course, also be necessary, as a t present, in order to reduce the acidity of the starch conversion liquor. Such materials as bentonite, colloidal aluminates (sodium aluminate and calcium aluminate produced by fusion of sodium carbonate or lime with aluminum oxide were studied
