SEPTEMB.ER 1947 Table 11.
633
Effect of High Concentrations of Oxygen on Burning Rate
Oxygen conrentration, 7' b y
voluriie 0 Burningrate,inchpersecond 0 38
5 10 15 0 . 3 8 0 39 0 . 4 2
20 0.52
25 0.67
30 1.00
Table 111. Comparison of the Burning Rate of a Powder Coated with Polyvinyl Alcohol and with yinylite (25' C., 1000 pounds per square inch) Burning Rate, Inch per Second Polyvinyl alcohol Vinylite 0.512 0 511 0.512 0 509 0 513 0 508 0,509 0 512 0.507 0 510 Av. 0.510 0 511
Different coating materials applied from different types of solution give the same burning rate, as shown by the data in Table 111. The burning rate is independent of the coating thickness, nithin wide limits (Table IV). The coating thickness must exceed a certain minimum value necessary to prevent irregular burning; too thick a coating may leave a troublesome residue and cause new irregularities. These coating experiments indicate that the coating acts only to sup-
Tahle IV.
Effect of Coating Thickness on Burning Rate (25O C., 1000 pounds per square inch)
KO. of Coats
Burning R a t e , Inches per Second Polyvinyl alcohol Vinylite 1.11 1 11 0.678 0 529 0.523 0 512 0.516 0 513 0.521 0 511 0.516 0 511 0.523 0 508
press the surface propagation of the flame and has no specific effect on the linear burning rate of the p w d e r . This method of measuring burning rates has been used successfully in a number of laboratories. The simplicity of the equipment, speed and precision of the measurements, and direct and unambiguous nature of the results obtained recommend it both for research purposes and for product control. LITERATURE CITED
(1) Muraour, H . , and Schumacher, W., -Vim. poudres, 37, 87-97 (1937). BASEDon work done for the Office of Scientific Research a n d Development under contract OELMsr-716 with the Gniversity of Minnesota and contract OEMsr-762 with t h e University of Wisconsin. I n p a r t from a thesis submitted t o the Graduate Faculty of the University of Minnesota by Clayton Huggett in partial fulfillment of the requirements for the degree of doctor of philosophy.
Determination of Antioxidants in Gasoline
,
LOIS R. WILLIARIS ANI BARYEY R. STRICKLAND Esso Laboratories, Process Division, Standard Oil Development Company, Elizabeth,
-4ntioxidant compounds are added to gasoline to inhibit the formation of gum and precipitation of lead and to maintain over-all stability. Alkyl-substituted p-aminophenol and p-phenylenediamine derivatives are the most commonly used inhibitors of high potency. Since many inhibitors may be lost from gasoline upon contact w i t h acid, alkali, or water, it is often important to check the amount of inhibitor present. This determination proved of value during the war in investigating the stability of
F
OR some time antioxidant compounds have been added to gasoline to inhibit the formation of gum and precipitation of lead, and to maintain the over-all stability. Alkyl-substituted p-aminophenol and p-phenylenediamine derivatives are a t present the most commonly used inhibitors of high potency. These materials are usually added in the concentration range of 1 pound per 5000 gallons of gasoline (2.4 mg. per 100 ml. is equivalent to 1 pound per 5000 gallons). Since many inhibitors may be lost from gasoline upon contact with acid, alkali, or wat,er, it is often important to check the amount of inhibitor present in a sample of gasoline. The analytical method presented proved of considerable value during the war in investigating the stability of aviation gasoline supplies, and is particularly useful in studying loss of inhibitor fromgasoline. Thc method for quantitatively determining the amount of aminophenol- and phenylenediamine-type inhibitors in gasoline \ Y ~ Sdeveloped by the Esso Laboratories from a procedure suggested by E. I. du Pont de Nemours and Company, based.on a reagent used by Folin and Denis ( d ) for indicating uric acid. Cortain other inhibitors, such as alkyl phenol derivatives, which are not extractable with acid or will not reduce Folin-Denis reagent citnnot tw determind in this manner.
N. J .
aviation gasoline supplies and is particularly useful in studying loss of inhibitor from gasoline. It is a colorimetric technique based on extracting amino-, phenol-, or phenylenediamine-type inhibitors from gasoline with aqueous hydrochloric acid solution, the hydrochloridesbeing formed. When the extract is neutralized with sodium carbonate in the presence of phosphotungstic acid solution, a blue coloration is produced which is proportional to the concentration of inhibitor present in the gasoline.
It is a colorimetric technique based on extracting the amino-, phenol-, or phenylenediamine-type inhibitors from gasoline with aqueous hydrochloric acid solution, the respective hydrochlorides being formed. When the extract is neutralized with sodium carbonate in the presence of Folin and Denis reagent (phosphotungstic acid solution), a blue coloration is produced which is proportional to the concentration of the inhibitor originally present in the gasoline. APPARATUS AND REAGENTS
Electric pH Meter. Instruments of the direct-reading type are preferable. Photoelectric colorimeter. Centrifuge. Hydrochloric acid, 5 5 aqueous solution. Sodium carbonate solution, 180 grams per liter. Folin and Denis Reagent. ,4 mixture of 100 erams of sodium tungstate, 750 ml. of Astilled water, and 80 m?. of 85% phosphoric acid boiled under reflux for 2 hours, cooled and filtered if necessary, and diluted to 1 liter. Reagents used must be free of nitrates, since nitric acid interferes with the color formation. Dye Solvent. A 1 t o 1 mixture of toluene and alkylate or isooctane. Diethyl ether may also be used. The solvent must be free of inhibitor.
V O L U M E 19, NO, 9
634
Table 11. Reaction of Various JIaterials with Phosphotungstic Acid Reagent
----
Material Tested Phenol Cresol p-Arninophenol Phenylenediamine ydroquinone Catechol Pvroeallol
fi
IO
0
I
1
0.1
0.2
I
I
I
0.7
0.8
0.9
IO
I O 12 1.4 17 MG / 100 M L . CONCENTRATION OF INHIBITbR
1.9
22
2 4
0.3
0.4
0.5
06
LBS /5000GAL
0
02
05
0.7
Figure 1. Measuring n-Butyl-p-aminophenol and N,N'Di-sec-butyl-p-phenylenediamine Inhibitors Using a Lumetron Photoelectric Colorimeter
Table I.
Analysis of Gasolines of Known Inhibitor Content
Inhibitor
Amount Added t o Gasoline Lb./6000 gal.
n-Butyl-paminophenol
0.50 0.50
1.00 1.00
N,N'-Di-ese-but&p-
phenylenediamine
1.00 1.00 1.00 1.00
Amount Found Lb./B000 gal. 0.52 0.55 0.98
0.97
0.96 1.02 0.96 1.04
Difference Lb./6000 gal.
0.02 0.05 0.02 0.03 0.04
0.02
0.04 0.04
PROCEDURE
Extract 100 ml. (or a smaller sample if the concentration of inhibitor is greater than 1 pound per 5000 gallons) of the gasoline to be tested with 20 ml. of 5y0 aqueous hydrochloric acid by shaking vigorously for 3 minutes in a separatory funnel. Draw off the acid layer and extract again with 10 ml. of the acid, shaking for 1 minute. Wash down the sides of the funnel with about 10 ml. of distilled water after each extraction and add to the acid extract. If the acid extract is colorless, proceed with the analysis; if it is colored, wash with successive 20-ml. portions of d e solvent until the color is removed. I f t h e inhibitor present is predominantly an aminophenol, add 5 ml. of the Folin and Denis reagent and by means of a pH meter bring the mixture to pH 7 by the addition of sodium carbonate solution with constant stirring. If the inhibitor present is a phenylenediamine, bring the solution to pH 7 before adding the Folin and Denis reagent and then add additional sodium carbonate to bring the solution to pH 8. Dilute the solution to 100 ml. with distilled water, mix, and if clear read per cent light absorption or transmittance immediately in a suitable colorimeter. If the solution is turbid a t this stage, centrifuge before the colorimetric reading. Concentration of inhibitor is read directly from a curve prepared for each inhibitor by measuring the absorption or transmittance for blue solutions developed when applying the test procedure to samples of benzene containing known amounts of the particular inhibitor. Figure 1 shows typical curves. Results are reported to the nearest 0.01 pound per 5000 gallons of gasoline. DISCUSSION
Both inhibitors and inhibitor solutions, to be used for making standard curves, must be pure, and since they are very active must be protected from light and air to prevent deterioration. I t has been found desirable to transfer portions of larger supplies of the inhibitors to small ampoules or bottles which are sealed with a nitrogen atmosphere and stored in the dark. Certain safety precautions should be observed when handling concentrated solutions as well as the pure aminophenols and phenylene-
Response t o Phosphotungstic Acid Reagent Negative Kegative Positive Positive Positive Positive Positive Kegative Positive Negative Negative Negative Positive Positive
diamines. If the inhibitor comes into skin contact, it should be removed immediately by washing thoroughly with alcohol. In conducting the analytical procedure, a blue color develops as pH 7 is approached if an aminophenoi inhibitor is present: whereas if the inhibitor is of the phenylenediamine type a pink color is formed a t about pH 5, a purple color develops upon the addition of the Folin and Denis reagent a t pH 7, and the solution becomes a clear blue a t pH 8. If, when a phenylenediamine is present, the Folin and Denis reagent is added before neutralisation, a red precipitate is formed that remains even a t pH 8 and spoils the determination. In the procedure followed by the authors, photoelectric colorimetric readings were taken using a red filter a t approximately 650-millimicron wave length, where absorption by the blue solution is in a constant and maximum range. Although the use of an electric pH meter and a photoelectric colorimeter, as described, is not absolutely essential, their use is preferred for accuracy and convenience. The pH may be regulated with pH paper and the color may be compared visually against that obtained froni samples of known inhibitor content. The pH should be regulated carefully, however, since the depth of color and the stability of the colored solution are markedly affected by pH. , When the electric pH meter and photoelectric colorimeter are used, the accuracy of the method is as indicated in Table I. The exact reaction which occurs between the phosphotungstic acid of the Folin and Denis reagent and the inhibitor is not known, although it has been established that the color is produced only in alkaline solutions. The best alkali for neutralization is sodium carbonate. Potassium carbonate or ammonia cannot be used because they form precipitates with the reagent (8). The color reaction apparently involves reduction by the inhibitor of tungsten oxides to blue tungstic oxides. In order to be measured by this method an inhibitor must first be extractable from the gasoline by hydrochloric acid and then must have a strong enough reducing potential to react with the phosphotungstic acid reagent. Many organic and inorganic compounds will respond to this reagent (Table 11). The presence in the gasoline of any material that will react with the reagent such as a-naphthol, catechol, or wood-tar distillate (which contains pyrogallol derivatives) would interfere with the test if a t all soluble in the hydrochloric acid solution. Alkyl phenol inhibitors and the usual additives in commercial gasoline such as dye and tetraethyllead will not interfere. Aged gasolines containing oxidized inhibitors may respond abnormally in the test, with poor reproducibility of results. ACKNOWLEDGMENT
The authors wish to express grateful acknowledgment to C. C. Hale and A. J. Jacobi for valuable suggestions and to Mrs. James Ling Chen for assistance in the laboratory experiments. BIBLIOGRAPHY (1) F o l i n , Otto, and Cicocalteu, Vintila, J . Biol. Chem., 73, 627-50
(1927). (2) F o l i n , Otto, and D e n i s , W., Ibid., 12, 239-43 (1912)
