Gum Stability of Gasolines J. W. RAMSAY, Research and Development, Department, Vacuum Oil Company, Inc., Paulsboro, N. J.
T
A study has been made of the variables in the of the flange. The top of the HE a c c e l e r a t e d oxidaoxygen bomb test for induction periods of gasobath was SO constructed as to fit tion test d e v e l o p e d by T'oorhees and E i s i n g e r snugly in a recess under the lines. The direct relationship between the in(5) showed that there mas a reflange of the bomb (notshownin lation between the oxidation of duction period a d the period of gum stability F i g u r e 1). E a c h b a t h w a s a gasoline and gum formation. has been conjirmed. A quantitative relationequipped with a n electric heater L i t t l e g u m was f o u n d in a ship between the induction period and the capable of bringing it to 100" C. sample under test Prior to the in about 15 minutes, and with oxygen pressure has been developed; this relaabsorption of o x y g e n . Hunn, lionship is independent of temperature. A a globe 'Ondenser to Fischer, a n d B l a c k w o o d (3) evaporation. For work a t temhas also been dece20ped between the peratures other than 100"c., a t h e n p r o p o s e d the m e t a l l i c oxygen bomb for work at higher induction period and the temperature. A new large oil-filled bat,hwasemployed method is proposed for extrapolating the results capable of holding all six bombs oxygen p r e s s u r e s . They deof bomb tests in order to estimate the stability of (FigureZ). veloped this method to a state Of good and 'Ongasoline at tenperature and pressure conditions This was thermostatically concluded that it would differentiate trolled, and efficient stirring was between a good and a bad encountered in practical storage. obtained by means of an electrically driven stirrer in a 3-inch l i n e from-the s t a n d p o i i t of gum stability. Using this method, Flood, Hladky, and brass tube, a. The 1000-watt three-way electric heater, b, was inside the tube; additional heat needed in bringing the bath Edgar (1) found that gum formation was always associated also rapidly up to temperature was supplied by a copper steam coil, c, with oxidation except in a few special cases. Herthel and beneath the false bottom, d. The bombs were supported on a Apgar (Z), using Voorhees arid Eisin- l/d-inch brass cover, e. The bath was insulated with magnesia ger's method, attempted t o correlate packing, f, and, while operating, the temperature was kept constant to 0.2' C. throughout the entire bath. The oil used storage with o x y g e n a b s o r p t i o n . was a water-white transformer oil with 0.1 per cent @-naphthol Mardles and Moss (4) d e v e l o p e d a added to reduce oxidation and corrosion. slightly different test for resistance t o An auxiliary bath for a mixture of ice and water was prooxidation, and attempted t o correlate it with storage. At the beginning of vided for use in cooling the bombs before filling and after the present work, it seemed desirable each experiment. The standard procedure adopted for filling the bomb was to start with a study of the accelerated oxidation test of Hunn, Fischer, and as follows: Blackwood. After thoroughly cleaning and drying the inside of the bombs, they were placed in the ice bath for a t least 45 minutes with the APPARATUSAND PROCEDURE covers in place. At the end of this time the covers were removed, a cork pad was placed in the bottom of each bomb, and an 8F o r t h e e x p e r i m e n t a l work, six ounce bottle containing 100 cc. of the gasoline to be tested was bombs were constructed of chrome- inserted in each. Before use, each 8-ounce bottle was cleaned with sulfuric acid and dichromate mixture, washed with distilled yanadium steel (Figure 1). water, and dried in an oven. Over the neck of each bottle was The wall thickness was about inch placed a parchment cap, made from a Soxhlet extraction thimble, and the inside diameter such that it in order to prevent contamination of the sample. The covers would accommodate an 8-ounce oil sam- were then put in place and made tight. The bombs, with the ple bottle with about '/16 inch clearance. samples inside, were allowed to stand in the ice bath for about The inside height of t,he bomb was about 15 minutes until the gasoline temperature dropped to approxi2 inches greater than the height of the mately 0' C. At this point the bombs were connected to an bottle. The bombs had flanges at the oxygen cylinder and oxygen, 10 pounds in excess of the desired top to which the covers were bolted witth pressure, was admitted. After cooling for 15 minutes, the pres'/?-inch cap screws. They were machined out of solid pieces of steel in order to FIGURE 1. D I . ~ G R A M ensure strength, although the present OF OXYGESBOMB work indicates that it would be satisfactory t o construct them from tubing Inside diameter, 2 inches. Copper coil, c by suitable insertion of a bottom and is shown vertical, b u t ib screwing on the flange. The joint benow used in horizontal tween t h e b o m b a n d t h e cover was position. made tight by means of a lead gasket s q u e e z e d down into a circular recesS by means of the cap screws, a. Each bomb was fitted with a pressure gage, b, attached to the bomb through an intermediate BOMBS FIGURE2. OIL B A T H FOR TESTING coil of l/8-inch copper tubing, t, to minimize condensation of gas'oline vapors in the gage. The oxygen tank was connected to sure was lowered to the exact experimental pressure; the bombs the bomb inlet by means of a brass pressure union, e, and '/ginch placed in the appropriate bath; and the experiment was copper tubing, through the needle valve, d, and a reducing valve were At the completion of the experiment, the bombs were (not shown in the figure). A safety valve was used in the oxygen started. again placed in the ice bath for about 15 minutes, after which the line to prevent putting excess pressure on the bomb. pressure was released and the samples removed. For esperiments at 100" C., a n individual water bath was provided for each bomb, which was immersed to within I inch
Experiments were always run in duplicate. The induction period was taken as the time interval between placing the
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data, although limited, confirm the findings by other investigators ( 1 , 5 ) .
$ I
0
g
EFFECT OF OXYGEN PRESSURE
P
c
By inspection of Figure 3, it is apparent that the induction period tends to increase with decreasing oxygen pressure. Since the gum stability of interest is under conditions of 1 atmosphere air pressure, and since the stability changes with pressure, i i m t in moue& the next step in the investigation was the FIGURE 4. G U M FORMATION 0s. IN study of the effect of pressure. Data a t OXYGENBOMB higher pressures t h a n 69 p o u n d s were TIME IN UOUPS Initial gage pressures at ice temperature, pounds FIGURE 3. PRESSURE-TIME CURVE OF obtained for t h e t h r e e g a s o l i n e s , and per square inch: a, 69; b , 34; c , 0. SAMPLES IN OXYGENBOMB Figure 5 shows that a s t r a i g h t line reproduces t h e results on e a c h g a s o l i n e bomb in the heating bath and the first evidence of pressure within experimental error. The linearity of this relation drop, minus a correction for the time required for the bomb to makes it possible to extrapolate to the induction period come to bath temperature. This correction factor will be corresponding to 1 atmosphere air pressure (approximately discussed in detail in another paper. 3 pounds per square inch absolute oxygen pressure). As a further verification of this relation between induction period and oxygen pressure, experiments were run on the RELATION BETWEEN INDUCTION PERIODAND GUM same three gasolines a t 100' C., using 69, 34, and 0 pounds STABILITY per square inch (gage) air pressure instead of oxygen. A While the work of other investigators mentioned in the first typical air pressure-time curve is shown in Figure 6. In paragraph showed a definite relation between oxidizing tend- the experiments with 34 and 0 pounds air pressure, the inency of a gasoline and its gum stability, the first step in the duction periods were not sufficiently well defined to be of any present investigation consists of a confirmation of this rela- value. The data obtained a t 69 pounds air pressure are also tion. I n this study, three 100 per cent cracked gasolines plotted in Figure 6 , the points being marked X where the air were used. Samples were placed in the bombs, and acceler- pressure has been divided by five to transform to oxygen ated oxidation runs were made a t 100" C. with three oxygen pressure. It is seen that they lie on the oxygen pressure line pressures in each case. The pressures used were 69, 34, and within the experimental error. All of the data thus far obtained had been a t 100' C., and 0 pounds per square inch (gage) a t the filling temperature of approximately 0' C. Since the vapor pressures of the gaso- accordingly experiments were made to study the effect of lines were very small a t this temperature, the above pressures pressure a t other temperatures. For this series, seven new were considered as oxygen pressures. I n the case of experi- samples were obtained. Samples 1, 2, 3, 4, and 6 were 100 ments a t zero pound gage pres- per cent cracked gasolines, and 5 and 7 were commercial sure, the air in the bomb was gasolines. For these experiments the oil bath was used to simply flushed out with oxygen. After filling, the bombs were placed in the water baths, and pressure r e a d i n g s w e r e taken a t r e g u l a r i n t e r v a l s , L x usually 15 minutes. Experi4 ments were made lasting 1,3,5, and 7 hours. At the end of I each run, the duplicate bombs I were cooled in ice and the samples r e m o v e d . Steam-oven I gum determinations a t 165" C. were made to determine the gum formed during each run. 0 1 t 3 4 HOURS T h e pressure-time d a t a , FIGURE 6 . PRESSURE-TIME CURVEFOR FIGURE 5. INDUCTION GASOLINEIN BOMBUSINGAIR INPERIOD us. OXYGENPRES- plotted, showed that after a STEAD OF OXYGEN SURE FOR THREE SAMPLESdefinite interval there was a disOF GASOLIKE tinct drop in pressure. Figure 3 i l l u s t r a t e s a pressure-time Pressure given represents initial y e a u r e at ice temperature. chart obtained from a complete heat the bombs; three oxygen pressures were employedoints marked x represent 100 pounds air pressure. set of runs on one gasoline. namely, 50,75, and 100 pounds per square inch (gage) a t 0" C. Here the I-., 3-., 5-. and 7-hour filling temperature. Pressure-time plots were made similar experiments are plotted on the same sheet. The milligrams to those in Figure 3, and the induction periods obtained. of gum per 100 cc. of gasoline are plotted in Figure 4 against Experiqents were run a t various temperatures between 80" time of oxidation in the bomb, This particular plot repre- and 120" C. The induction periods found for each sample a t sents the same sample of gasoline referred to in Figure 3. each temperature and pressure studied are given in Table I. The other two gasolines used in this series of experiments gave By plotting the induction period against the pressure, the similar results. Comparing the induction periods with the same increase with decreasing oxygen pressure was found as gum stability as shown in Figures 3 and 4, it is observed that was shown in Figure 5. By extrapolating these lines, the the two sets of time intervals are in good agreement. These value a t each temperature for the induction period under 1
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I
3 3
INDUSTRIAL AND ENGINEERING
May, 1932
atmosphere air pressure was obtained. These values are also given in Table I.
FIGURE 7. INDUCTION PERIOD AT 100 POUNDS PER SQUARE INCH OXYGENPRESSURE us. EXTRAPOLATED VALUES FOR INDUCTION PERIOD UNDER 1 ATMOSPHERE AIR PRESSURE (ABS.) AT SAME PERATURE
Reaults from aeven gasoline samples taken over a temperature range of 8O-liO0 C.
An analysis of the data given in Table I indicates a simple mathematical relation between the extrapolated induction period under 1 atmosphere of air and the induction period under 100 pounds per square inch oxygen pressure. This relation is given graphically in Figure 7. This plot shows that, independent of the temperature, the induction period a t 1 atmosphere air pressure is about 41 per cent greater than the induction period under 100 pounds oxygen pressure: Iatm. air
= 1100 pounds oxygen
x 1.41
(1)
This clearly shows that oxygen pressure plays a relatively small part in the bomb test, and it would seem that, in the interest of safety, much lower pressure could be used. However, the pressure is necessary to make the breakdown point sufficiently sharp to be observed on the gage.
TABLE I. INDUCTION PERIOD AT VARIOUS TEMPERATURES AND PRESSURES
GASOLINE
TEMP.
la
120 110 100 90 80
OXYQEN PRESSURE 100 Ib. 75 lb. 50 lb. Hours Hours Hours 0.2 0.3 0.4 0.9 1.1 1.3 3.95 2.95 3.45 9.8 8.2 9.0 25.2 21.2 23.2
2"
120 110 100 90 80
0.6 1.5 4.2 10.2 23.7
30
120 110 100 90
0.9 2.5 6.9 16.5
4a
120 110 100 90
0.5 1.3 4.0 10.4
5b
120 110 100 90
6a
100 90 80
O
541
EFFECTOF TEMPERATURE From the data presented in Table I, it is apparent that a t any given oxygen pressure the induction period decreases very markedly with an increase in temperature. This suggested a means of predicting the gum s t a b i l i t y a t temperatures found in practical storage, for if the induction period a t atmospheric p r e s s u r e of air could be plotted against t e m p e r a t u r e in such a manner as to permit extrapolation, it would be possible to estimate the induction period a t any temperature. I n Figure 8 the induction periods at 1 atmosphere air pressure ( c a l c u l a t e d from Equation 1) of the seven s a m p l e s of g a s o l i n e tested are p l o t t e d on a semi-logarithmic c h a r t against the absolute temp e r a t u r e . For e a c h sample it is found that the log of the induction is a linear function of the FIGURE 8. INDUCTION PERIOD UNDER ATMOSPHERIC AIRPRESSURE temperature. The given us. ABSOLUTE TEMPERATURE FOR equation of these plots is SEVENSAMPLES OF GASOLINE log1 - = u - bT (2) . . where I = induction period at 1atm. air pressure T = absolute temperature a and b = constants, specific for each gasoline Table I1 gives these constants for the seven samples tested. TABLE11. CONSTANTS FOR EQUATION 2 aABOL1NE
0
1 2 3 4
17.345 16.194 16.214 17.135
b 0.0449 0.0387 0.0409 0.0440
GASOLINE a b 5 17.495 0.0449 6 19.162 0.0528 7 13.716 0.0361
ATM. AIR
PRESSURE
Houre 0.7 1.8 5.1 11.6 30.1
0.7 1.7 4.7 11.2 25.7
0.8 2.0 5.2 12.2 27.7
1.0 2.2 6.5 14.7 32.7
... ... ...
1.0 2.9 7.8
1.2 3.3 8.9
0.6 1.45 4.75 11.2
0.7 1.6 5.7 12.1
0.5 1.3 4.25 11.3
... ... ... ... ... ... ... ...
0.6 1.5 4.8 12.0
0.7 1.75 5.7 12.9
0.2 0.7 2.5
0.3 0.8 2.7
0.4 1.0 3.0
0.7 1.3 3.4
110 0.6 0.8 1.5 100 1.2 90 2.9 3.5 100% cracked. b Commercial sample.
1.0 1.7 4.0
1.5 2.4 5.2
7b
a
c.
CHEMISTRY
A study of the data obtained indicates that the slope of the semi-logarithmic plot varies with different gasolines in such a manner that more than one temperature point is necessary in order to make possible a prediction of gum stability a t storage temperatures. It would be necessary to determine the induction period a t two (and preferably more) temperatures for the prediction of gum stability of a gasoline in storage. CONCLUSIONS 1. The induction period and period of gum stability of a gasoline a t a given temperature are a linear function of the oxygen pressure. 2. The induction period of a gasoline and the period of gum stability a t any given oxygen pressure are a function of the temperature. 3. It seems quite probable that, if the induction periods a t two or three temperatures and under 100 pounds oxygen pressure are known for a sample of gasoline, its period of gum stability under atmospheric pressure of air and a t any temperature may be predicted with a fair degree of accuracy. The validity of this conclusion is being investigated by gum stability experiments a t atmospheric temperatures.
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(4) Mardles and Moss, J . Inst. Petroleum Tech., 15,657, 673 (1929). and Eisinger, J . SOC. A~~omotiWE a , 24, 5@-92 d paper ~ presented ~ ~ before , ~ i of ~ (5) . Voorhees (1929). Petroleum Chem., 80th Meeting of Am. Chem. SOC.,Cincinnati, Ohio, September 8 t o 12, 1930. (2) Herthel and Apgar, Oil Gas J.,28, 136 (Deo. 5, 1929). RECEIVED August 24, 1931. Presented before t h e Division of Petroleum (3) Hunn, Fischer, and Blackwood, J. SOC.Automotive Eng., 25, Chemistry at t h e 82nd Meeting of t h e American Chemical Society, Buffalo,
LITERATURE CITED
(1) flood, ~ l ~ d and k ~ ~,
3 1 (1930).
N.Y., August
31 t o September 4, 1931.
Composition of Straight-Run Pennsylvania Gasoline 11. Fractionation and Knock Rating M. R. FENSKE, D. QUIGGLE,AKD C. 0. TONGBERG School of Chemistry and Physics, Pennsylvania State College, State College, Pa.
P
by the Ethyl Gasoline LaboraENKSYLVAKIA straightI n one fractionation, straight-run Pennsylvania tories. For some p u r p o s e s i t r u n g a s o l i n e h a s been gasoline was separated into fractions of alternate fractionated by means of may be better not to add lead high and low knock rating. It was found that to the sample being rated, but the 27-foot and 52-foot columns this variation in knock rating was due to straightrather to match its rating with described in a previous paper (3). chain parafins and to aromatic and naphthenic other s t a n d a r d i z e d fuels in It is hoped that the results obterms of octane number. Since tained will furnish fundamental hydrocarbons being concentrated in certain fracboth r a t i n g s are n e e d e d , this information on the composition tions. Refractionation enabled some substances point is discussed later in conof the gasoline and may be the to be obtained which closely approximated pure nection with Figure 6. means of i m p r o v i n g its antimaterials, both as to physical properties and knock qualities. FR.4CTIONATION OF 510" F. knock behavior. A n y one normal parafin is Two b a r r e l s of crude petroEXD-POINT GA~OLIXE leum were obtained from flooded present in the Pennsylz'ania straight-run gasoline S i n e gallons of the 510" endwells on the Jones Lease, Rew to the extent of 2 to 5 per cent. It is very likely point gasoline were charged into C i t y , l o c a t e d about 5 miles that these normal para#ns, while not constituting the 2i'-foot, 3 - i n c h d i a m e t e r south of Bradford and belonga very large percenlage of fhe gasoline, are largely column. A total condenser was ing t o t h e K e n d a l l Refining responsible for the knock. The fractionating used, a n d t h e f r a c t i o n a t i o n Company of Bradford, Pa. This carried out a t about 20-30 to 1 crude oil w a s b a i l e d out of a equipment used, effectively concentrated these reflux ratio (liters of reflux to run tank, placed in clean drums, parafins and permitted their removal from the liters of product). The remains e a l e d , a n d s h i p p e d to the gasoline. der of the operating details have l a b o r a t o r y . T h e c r u d e oil been described previously ( 3 ) . was t o w e d bv a simde batch distil1at:on in "order to obtain the gasoline. A considerable Complete data on this fractionation are &own in Figure 1. amount of low-boiling material came off of the crude a t the The distillation ranges of the charge, distillate, and blended beginning of the distillation. This was condensed by means samples are also indicated. The boiling point (at about 737 of Dry-Ice in a container capable of withstanding pressure. mm. pressure), specific gravity, (diO,), refractive index, These light ends were not investigated, since they were known (n':), and knock rating (cubic centimeters of tetraethylto consist of propane, butane, and pentane. The distillation lead) are plotted against the percentage of total charge was carried on into the kerosene to ensure the removal of all distilled over. I n the rectification, 165 fractions were the gasoline from the crude. This distillate, comprising 39 collected, but knock tests were made on only 35 samples. per cent of the crude, is called, for the purposes of identifica- The fractions indicated by horizontal lines on the knock curve tion, 'L5100F. end-point gasoline." were blended, and the resulting samples tested as a whole in order to reduce the number of knock tests required. METHODOF RATING KNOCK I n Figure 1 the first 5 per cent represents propane and The knock ratings were obtained on a Delco-Light knock- butane, principally, and some pentane which were condensed testing engine which had been used by the Ethyl Gasoline by means of Dry-Ice. These light ends are, of course, very Corporation prior to the Series 30 model. This engine was valuable, since their knock rating is zero or better. procured through the cooperation of Graham Edgar. All The plot shows clearly in which fractions of the gasoline the knock tests are referred to Ethyl Standard, 74 octane number. knock is greatest, and that there are alternately good and The rating indicates the number of cubic centimeters of bad fractions. It is of particular interest to note that the tetraethyllead (not Ethyl fluid) required to make a given curves of refractive index and density are the reverse of the fraction or gasoline equal to Ethyl Standard. I n some in- knock curve. I n each of the peaks of the density or refractivestances, fractions are better than Ethyl Standard. I n such index curves are concentrated the aromatic hydrocarbons of cases they are given as negative ratings, and lead is added to that particular boiling point. The valleys do not contain any the Ethyl Standard to equal the fraction being tested. The aromatics. Obviously then, since the aromatic hydrocarbons test procedure followed was the bouncing-pin method used do not knock, the peaks in which they are concentrated will be
