April, 1933
INDUSTRIAL AND ENGINEERING CHEMISTRY
or plates the ink film is of sufficient thickness to permit such surface concentration, but on paper the ink film is not only much thinner but is absorbed so that this surface action is a t least reduced. It remains for more effective antioxidants to be found. It would be possible to relate many other printing ink problenis, but the few that have been mentioned niay serve t o
381
indicate their variety and range, Like many another chemical industry the printing ink industry uses a great variety of raw materials that in several instances are of unknown composition. The building of a scientific foundation is naturally a slow process, but one in which definite progress is being made. October 31, 1932,
Distribution of Gum-Forming Constituents in Cracked Gasoline S. &I.MARTIN,JR..WITH W. ,4.GRUSEAKD ALEXANDER LOWY University of Pittsburgh and Mellon I n s t i t u t e of Industrial Research, Pittsburgh, Pa.
T
the a p p l i c a t i o n of a suitable HE revival of interest in The oxygen stability at low temperatures of oxidation test to carefully sepahighly cracked gasoline, narrow-boiling fractions of a vapor-phase disrated close f r a c t i o n s of such a of the so-called vapor tillate has been studied. The amount of g u m gasoline might give interesting phase t y p e , which o c c u r r e d formed is found to vary greatly f r o m one fraction results. Support for this belief a b o u t 1926, has prompted a to another. Gum is obtained f r o m the fractions was found in work by blardles great deal of work on the refina n d M o s s (IO), R u e a n d ing of this material. In general, boiling between the limits 62.8" and 146.1" C. Espach (18), and Cassar (7). the results have not been en(145" and 295" F.) with definitely larger amounts M a r d l e s and Moss a p p l i e d tirely s a t i s f a c t o r y . The raw in fractions with boiling points 73.9" to 79.4" C . the copper dish test and Cassar gasolines are objectionable as (165" to 17.5" F.), 101.7" to 107.2' C. (215" to the oxygen stability test to 10 to color, odor, and i n s t a b i l i t y 225" F.), and 123.9" to 129.4" C. (255" to per cent cuts of a cracked gasoto o x i d a t i o n . The o r d i n a r y line, and Rue and Espach obrefining methods yield products 265" F.). The shape of the gum curce indicates which may be t o l e r a b l e while served the conduct on storage of that this gum formation is due direcily or inboth 10 and 4 per cent cuts of fresh, but w h i c h develop gum directly to specific compounds which ure thought a s i m i l a r material. Both the a n d lose a n t i k n o c k value in to be conjugated diolefins. c o p p e r d i s h and the oxygen storage. D r a s t i c t r e a t m e n t Treatment with maleic anhydride and with will produce gum-free and stable gum tests are c a r r i e d on a t 100" C., and it is obvious that gasolines but a t the cost of consulfuric acid, and also partial hydrogenation siderable volume losses and an significant r e s u l t s c a n n o t be render the fractions stable to a 38" C. oxidation appreciable diminution in antiexpected for f r a c t i o n s boiltest. This is probably due to the removal of knock value. W h i l e v a p o r ing below that temperature becery reactiae unsaturated hydrocarbons which p h a s e g a s o l i n e is now widely cause of rapid e v a p o r a t i o n in f o r m peroxides readily. The latter in turn act marketed, the usual procedure is the one case and of vapor-phase to mix it with more stable prodo x i d a t i o n in the other. Rue as oxidation catalysts. These treated materials ucts such as uncracked gasoline. and Espach depended on the when oxidized at 50" C. give appreciable amounts Thus, in one way or a n o t h e r , s e p a r a t i o n of insoluble gum, of gum, and this is attributed to the oxidation of the a n t i k n o c k value which is which is a strictly qualitative certain unsaturated hydrocarbons still present, the chief advantage of this type test that does not indicate the such as the cyclic olefins. of fuel is not fully available to actual a m o u n t of gum in the the ultimate consumer. fractions. Both gum formation and decrease in antiknock value during The acquirement of desired information on the distribustorage seem t o be attributable to oxidation of t,he gasoline. tion of gumming constituents depends on adequate fractionaThe use of accelerated oxidation tests for predicting the gum tion and on the devising of an accelerated test resembling as stability of a motor fuel is well established, and it has re- much as possible the conditions of ordinary storage. As to cently been stated (11) that the same procedure can be used fractionation, not only should the separation be as sharp as to estimate the extent to which deterioration of antiknock possible, but it was believed that the choice of fractions should value will occur. The oxidizable character of cracked gasoline be determined on boiling point rather than arbitrarily by is well known, and this indication of unsaturation is ordinarily volume, as was done in the studies just cited. Cutting by attributed to a high olefin content. The term should un- temperature seemed likely to be more effective in keeping doubtedly be understood to include not only diolefins but also in one fraction the whole amount of each constituent. cyclic olefins and olefins attached to aromatic nuclei. iipThe inconsistency of testing for oxidation a t 100" C. a parently it should also cover compounds of the type of 1,2- series of fractions, some boiling below and some above that dimethylcyclopentane and 1,2-dimethylcyclohexa1ie, recently temperature, has already been mentioned. Such a method of shown by Chavanne (8) to be oxidized in air a t their boiling test is entirely logical for comparing a series of whole gasopoints. lines, for the proportion vaporized is not likely to differ greatly The unsaturated portion of a cracked gasoline is probably in one case from that in another. But the results of a test made up of many types of hydrocarbons that differ in their re- a t one temperature are not strictly comparable for a series activity to oxygen. It therefore occurred to the authors that of materials of different boiling points, such as the groups of
INDUSTRIAL AND ENGINEERING CHEMISTRY
fractions studied in this work. For such a comparison the materials under test should either be entirely in the liquid phase or entirely in the vapor phase. For this study the former alternative was adopted; but, as is obvious, a compromise was necessary between the vaporizing tendency of the hydrocarbons and the decreasing reactivity with lowered temperature. Testing a t 25" and 38' C. was finally adopted. The very low-boiling fractions still have appreciable vapor pressure a t these temperatures-a fact that means that some oxidation in the vapor phase is possible. It is believed, however, that the best compromise has been chosen. TEMPERATURE"c.
Vol. 25, No. 4
The product just described was distilled through a column essentially the same as that described by Peters and Baker (17). The reflux ratio was slightly above 10 to 1, and a fraction was taken for each 5.6" C. (10" F.) rise in temperature as read from an A. S. T. M. Fahrenheit thermometer. Thirtytwo such fractions were collected to a final boiling point of 201.7' C. (395" F,). The rate of distillation was approximately one cc. per minute. The fractions were immediately put under an atmosphere of nitrogen and stored in a refrigerator a t about 5" C. (41' F.) until ready for use. In Figure 1 is given the distillation curve obtained by plotting the volume of the 5.6' C. (10" F.) fractions against the mid-point of the boiling range of the fraction. The degree of segregation attained, as evidenced by the shape of this distillation curve, is rather striking. Iodine numbers ( I S ) , iodine substitution values ( I S ) , and specific gravities by pycnometer were determined on each fraction; these data are given in Table I. Peaks in the specific gravity values a t boiling points 73.9" to 79.4", 101.7" to 107.2', and 140.6' to 146.1" C. (165" to 175")215" to 225", and 285" to 295°F.) are clearly defined. The iodine numbers drop off with increasing boiling point, there being no sharp breaks a t any points. TABLEI. PHYSICAL AND CHEMICAL PROPERTIES OF FRACTIONS
TEMPERATURE OF.
FIGURE1. DISTILLATION CURVE
Another reason for selecting a low temperature for testing lies in the greater resemblance to the conditions of storage. It is possible that a t 100" C. reactions will occur which do not take place in storage. In order to compensate for the slow reaction velocity a t the lower temperature, it mas decided to use oxygen under pressure.
EXPERIMEKTAL PROCEDURE The vapor-phase distillate employed was made by cracking a light solar oil on a commercial scale in a full-size cracking unit. The still was operated a t about 600" C., and the oil, under 7 kg. per sq. cm. (100 pounds per square inch) pressure, was exposed to this temperature for a time estimated to be about 10 minutes. The distillate so produced possessed a light yellow color and a disagreeable odor characteristic of products cracked in this manner. This product had the following general properties: 1.
Distillation range ( 2 ) : 29.4 92.2 136.7 188.9 201.1 207.8 96.5 1.5 2.0 0.7742 (50.5) 115.3
Mrtiimum temp., Total amount over, Residue, % Loss, % 2 . Specific gravity, d i 0 (" A. P. I . a t 60' F.) 3. Iodine number (Hanus) 4 . Iodine number ( 1 3 ) : 64.2 -4ddition value 25.5 Substitution value 0.23 5. Sulfur (lamp method, S), % 6. Preformed gum (Cooke's steam oven method, Q), 21.8 mg./100 cc.5 7 . Oxygen gum (do) obtained when sample of 011 is heated In atmosphere of oxygen a t 100' C . for 1850 5 hours, mg./100 cc. 4109 8. Copper dish gum ( 4 ) , mg./100 cc. 9 . A sample of distillate when exposed t o sunlight deposited a large amount of gum within 6 months. Another sample which was stored under nltrogen a n d exposed under same conditlons has not deposited gum after 18 months. a I n order to permit correlation of this work with previous research, the gasoline used was one which had been preserved in 5-gallon black bottles completely filled a n d set aside in a cool place for a period of 8 months. While some incrkase in t h e content of the preformed gum occurred during this time separate experiments on fresh materlal from t h e same source showed t h a t gum formation occurred f r o m the same fractions and to the same relative extent (Figure 3, curve for V. P. D . lot B ) .
FRACTIOX BOILIXQ POINT F. c.
[ODINE IODINE % OF TOTAL SP. GR., ADDI- SCBSTIVOLUME T I O N T UTION dzo
1 2 3 4 5
67- 85 85- 95 95-105 105- 115 115-125
19.429.435.040.646.1-
29.4 35.0 40.6 46.1 51.7
2.33 0.92 0.70 0.50 0.40
0.6430 0.6436 0.6436 0.6651 0.6693
214 217 218 201 187
2.5 1.9 2.5 3.3 3.3
6 7 8 9 10
125-135 135-145 145-155 155-165 165-175
51.757.262.868.373.9-
57.2 62.8 68.3 73.9 79.4
0.57 1.60 3.10 2.80 1.53
0.6717 0.6780 0.7014 0.7241 0.7390
170 157 137 120 116
4.2 4.5 8.9 18.9 20.2
11 12 13 14 15
175-185 185-195 195-205 205-215 215-225
79.4- 8 5 . 0 85.0- 90.6 90.6- 96.1 96.1-101.7 101.7-107.2
0.85 2.30 3.70 3.90 3.30
0.7369 0.7300 0.7354 0.7496 0.7605
101 93 83 82
2i:4 24.4 27.1 27.3
16 17 18 19 20
22 5-2 35 235-245 245-255 255-265 265-275
107.2-112.8 112.8-118.3 118.3-123.9 123.9-129.4 129.4-135.0
3.17 3.33 3.37 3.90 4.90
0.7586 0,7576 0.7659 0.7770 0.7843
79 72 66 59 51
27.0 30.8 31.0 30.0 30.3
21 22 23 24 25 26
275-285 285-295 295-305 305-315 315-325 325-335
135.0-140.6 140.6-146.1 146.1-151.7 151.7-157.2 157.2-162.8 162.8-168.3
4.47 1.97 3.23 3.23 4.00 4.12
0.7858 0.8058 0.7918 0.7983 0.8045 0,8108
53 47 45 42 37 31
29.5 30.5 31.1 28.0 28.0 28.0
27 28 29 30 31 32
335-345 345-355 355-365 365-375 375-385 385-395
168.3-173.9 173.9-179.4 179.4-185.0 185,O-190.6 190.6-196.1 196.1-201.7
3.23 2.27 4.07 2.60 3.07 2.87
0.8154 0.8201 0.8263 0.8343 0.8457 0.8551
29 26 22 17 18 13
28.5 28.0 27.5 28.0 25.0 25.0
...
The oxidation test used to measure the stability of the fractions toward gum formation, developed for the purpose of this investigation, was carried out in small 200-cc. iron bombs, the details of which are shown in Figure 2. In making the tests, 2.5 cc. of the liquid were put into a 2ounce (60-cc.) oil sample bottle, which was then placed in the bomb. A small test tube containing a little water was inserted in the bomb for the purpose of saturating the atmosphere above the sample with moisture, thus maintaining constant humidity. At the start of the tests, oxygen to 1 kg. per sq. cm. (15 pounds per square inch) was put in the bombs, which were placed in a constant temperature oven at 38" C.; and, after allowing 4 hours for the proper temperature adjustment, the oxygen pressure was raised to 1.4 kg. per sq. cm. (20 pounds per square inch). The bombs were kept at 38' C. for one week (168 hours). During the course of the test, the pressure was read twice daily from a master gage, which was mounted in such a position that the bombs could be attached to it by means of a union that
April, 1933
INDUSTRIAL AND ENGINEERING
screwed directly to the free end of the valve, without removing them from the oven. At the end of the test period the bombs R"ere cooled to room temperature, the pressure released, the bombs opened, and the samples t,ransferred to 50 X 30 mm. crystallizing dishes. The bottles were washed out with acetone, and the samples and acetone washings evaporated in a steam oven. The residues remaining were then dried at 110" C. and weighed. These weights are expressed in terms of gum numbers, one gum number equaling one mg. of gum per 100 cc. of sample.
\
The method as conducted a t 38" C. cannot be used for ascertaining t'he oxidation susceptibility of the very low boiling fractions, if the oxidation thereof is to be confined to a liquid-phase reaction, because certain of them boil below that temperature. For satisfactory handling of these lower boiling fractions, the temperature was dropped to 25" C. and the time extended to 2 weeks. These low-temperature experiments were carried out in a water bath maintained a t 25" C., and the pressures were not read during the period. The procedure otherwise was as described. Oxidation tests were conducted on fractions 7 t o 32, inclusive, a t 38" C., and on fractions 1 to 16, inclusive, a t 25" C. The gum data from these tests are given in Figure 3 (curves for V. P. D. lot A ) . The distribution of oxidizable constituents was checked with a second lot of the vapor-phase distillate produced a t a later date. The data from this second material are given by the curve for V. P. D. lot B in Figure 3 . This curve has the same peaks and dips as the curve for V. P. D. lot A a t 38" C. The curve for the samples oxidized a t 25" C. has the same characteristic peaks as the 38" C. curve, although the values are not quite identical. The peaks a t fractions IO and 15 on this curve, while not as great in magnitude as the peaks on the 38" C. curve, are just as pronounced. This finding can readily be understood when it is pointed out that the reaction was carried out a t a lower temperature and that the reaction was therefore less advanced. To be absolutely certain that the gum found in the fractions was the result of oxidation and not due to preformed gum present in the samples before they were put into the bombs, the entire series of fractions was tested for preformed gum by evaporating 2.5-cc. portions of each fraction from glass dishes in a steam oven. I n all cases the dishes were clean, and no weighable amount of gum was found. That this gum formation is primarily the result of oxidation is borne out by the fact that those fractions which absorb the greatest amount of oxygen also give the largest amounts of gum. The sensitivity of the test is shown by the wide difference between the amounts of gum formed by the individual fractions and by the fact that the whole distillate, when oxidized under the same conditions, gave a gum number of the order of 20. The entire distillate, however, yielded larger quantities of gum when tested under more severe conditions, a fact that is demonstrated by the data on the properties of the starting material. This low gum figure from ttie whole distillate is no doubt due to the low concentration of the gumforming constituents therein as compared with the more concentrated amounts that are found in the narrowboiling fractions that form gum.
TENTATIVE EXPLANATION OF ORIGINOF GUM I N UNSTABLEFRACTIONS The fact that the individual 5.6' C. (10" F.) fractions show such wide variations in gum formation suggests that this instability is due to specific compounds that boil close to or within the range covered by the fractions. Flood, Hladky, and Edgar (12) from work on pure hydrocarbons were led to believe that aliphatic and cyclic diolefins and also mono- or diolefins attached to a benzene ring are the
CHEMISTRY
383
substances mainly responsible for gum formation in gasolines; 1,5-hexadiene, however, was more stable than the other diolefins. That the different diolefins vary somewhat in their reactivity toward oxidation is also shown by the work of Kogermann (16) on the autoxidatioii of these hydrocarbons. He found that the conjugated compounds absorb oxygen readily, whereas 1,j-hexadiene in oxygen a t 19" to 27" C. showed no oxidation in 3 months. There is evidence available (19, 21) which suggests that the cycloolefins are also gum formers under certain conditions. The present investigation revealed that cyclohexene in 50 per cent concentration in a fraction of corresponding boiling point from a
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60MB ATTACHED TO QAWE FOR PRESSURE READING
FIGURE 2. DIAGRAH O F APPARATUS straight-run gasoline gave no gum in the 38" C. test if peroxides were removed before testing. When a small amount of oxidized gasoline was present, a gum number of 68 was obtained. Corresponding tests with diisobutylene and 2-octene showed that a t 38" C. and in 50 per cent concentration these hydrocarbons gave no gum even when peroxides were added in the form of a small amount of oxidized gasoline. The results of Flood, Hladky, and Edgar are more or less typical of a large volume of literature on the gum-forming tendency of pure hydrocarbons-cyclic olefins and conjugated diolefins being chiefly suspected. The boiling points of all the known compounds of these classes' were therefore compared with the boiling points of the gum-forming fractions designated by the curves on Figure 3, and it was found that every fraction forming appreciable amounts of gum corresponded in boiling point to one or more conjugated diolefins. I n addition, most of the cycloolefins that are described in the literature have boiling points within the range of the principal gum-forming fractions (Figure 3). The cycloolefins with boiling points above the limits for fraction 25 are compounds of seven- or eight-membered rings or seven-membered rings with a number of alkyl groups in the side chain. Compounds of this structure are unstable according to the Baeyer strain theory, and would hardly be present in a product that had been subjected to the conditions under which vapor-phase cracking takes place. This distribution of the cycloolefins is interesting in that it practically parallels the distribution of the gum and may explain in part why these fractions yield such large quantities of gum once they start oxidizing. I A list of hydrocarbons with their boiling point%,specific gravities, refractive indices, and literature references is contained in the thesis of S. M . Martin, Jr.
384
I N D U ST R I AL A N D
E N G I K EER IM G C HE M ISTR Y
Possible irregularities due t o the occurrence of these various compounds in constant-boiling mixtures should be kept in mind. The detailed data that show the above interesting correlations are given in the thesis from which this paper is taken. To illustrate this point the following examples are given. The curves in Figure 3 show fractions 10, 15, and 19 to be
Vol. 25, No. 4
tically insoluble in gasoline, the liquid can be filtered from the solids, washed with alkali t,o remove any dissolved anhydrides, and redistilled for further purification. Those fractions with boiling points within the range known to give the largest amounts of gum were therefore treated with maleic anhydride, according to the following procedure : Twenty-five cubic centimeters of the fraction and 5 grams of maleic anhydride were put into a 250-cc. flask and stoppered with a cork carrying a reflux condenser; the flask and contents were heated in a water bath at 60' C. for 4 hours. During this eriod the flask was shaken occasionally t o bring the molten angydride and oil into better contact. -4fter this heating period, the flask was cooled to 0' C.; the liquid was decant,edfrom the solid material and washed once with water, twice with 15-cc. portions of 10 per cent sodium hydroxide, and then twice with water. The treated material was redistilled. Portions of these treated fractions were tested for stability at 38' and 50' C. by oxidizing them for one week under 1.4 kg. per sq. cm. (20 pounds per square inch) oxygen pressure as above and weighing the gum formed. These data are given in Table 11. T.4BLE
II.
GUM FORMED IN FRACTIOXS OF VAPORPHASE DISTILLATE4
(Samples oxidized under 1.4 kg. per sq. cm. oxygen pressure for 168 hours a t temperature indicated) GCM F R O M
Gnu FROM
GUMF R O M FRACTIONS v. P. D
OB
FRACTION N U M ~ E R
FIGURE 3. GUM CURVESFOR VAPOR-PHASE DISTILLATES
relatively more unstable than the others. These fractions cover temperature ranges in which the following diolefins and cycloolefins may be expected t o diptil, if present in the gasoline: RECORDED BOILING POINT
HYDROCARBON FRACTION 10. BOILING P O I N T 76'
TO 81'
c.
C."
2-hlethyl-2,I-pentadiene 2-Methyl-1,3-pentadiene 1,l-Dimethylcyclopentene ?,4-Cyclohexadiene m-Dihydrobenzene 1.3-Cyclohexadiene FRACTION 15. BOILING P O I b T 104'
74 75-77
E.5 80.5 80.5 TO 108'
C.'
103 103 10 6 107 107-9 10s 10s 110
1-Ethylcyclopentene 1-Methyl-3 5-cyclohexadiene
l-Methvl-l:3-~vclohexadiene FRACTION 19. BOILING POINT 127'
a
TO 13'2'
C.'
2 5-Dimethyl-2 4-hexadiene 2:1Llethyl-3-eth$l-1,5-hexadiene 1 4-Dimethyl-1-cyclohexene 1:3-Dimethyl-1,5-cyclohexadiene Corrected for emergent stem and barometric pressure.
125-30 127 127.4 130
EFFECT OF REMOVING CONJUGATED DIOLEFIKS ON Guhl FORMATION From the above points it seems obvious that, if the conjugated diolefins that are thought to be present in the unstable fractions are responsible for their instability, a removal of these compounds should affect the rate a t which the fractions form gum, Diels and Adler (10) have shown that conjugated diolefins react readily with maleic anhydride to give definite compounds. Birch and Scott ( 5 ) have made use of this reaction to isolate a number of diolefins from a compression-plant gasoline. The compounds formed as a result of the reaction between the diolefins and maleic anhydride are for the most part crystalline solids of definite melting points; in most cases they can be easily hydrolyzed to the corresponding acids. This reaction offers a possible means of removing conjugated diolefins from a cracked gasoline; after treatment with maleic anhydride, which is prac-
c. 9 10 11
68.3- 7 3 . 9 73.9- 7 9 . 4 79.4- 8 5 . 0
Ma./i00 cc. .. OC 16 0 1300 0 1548
Ma./i00 cc. .. 136 .. 166 0 180 ..
1298 2568 1134
12 13 14
85.0- 9 0 . 6 90.6- 9 6 . 1 96.1-101.7
4 4 20
1152 1448 1648
168 284 272
0 335 200
632 822 1926
15 16 17
101.7-107.2 107.2-112.8 112.8-118.3
40 8 4
1468 1520 1920
450 400 208
1008 644 250
2798 2134 1820
18 19 20
118.3-123.9 123.9-129.4 129.4-135.0
0 12 0
1024 1744 1040
400 328 320
540 130 50
1964 2372 1770
21 22 23
135.0-140.6 140.6-146.1 146.1-151.7
.. ., ..
..
220 236 240
40 0
732 98 66
'
.. ..
.. 320 52 24 151.7-157.2 .. 44 .. 240 25 157.2-162.8 .. Vapor-phase distillatd = V P. D b Acid-treated and hydrogenated materials gave no weighable amount of gum under conditions of 38' C test In the cases ahere zero gum numbers are reported, the oxidized samples did not deposit an amount of gum that could be detected In order t o avoid the possibility of atmospheric oxidation during treatment, duplicate experiments were made in which portions of the fractions were treated with maleic anhydride in sealed tubes in an atmosphere of carbon dioxide a t 70" C. The results differed in no way from those obtained by refluxing. The effect of removing the conjugated diolefins on gum formation can be seen by comparing the data from the 38" C. test on the samples treated with maleic anhydride with the data for the corresponding untreated fractions, as given in Table 11. That maleic anhydride, if not completely removed from the fractions, does not act as an antioxidant was proved by the fact that maleic anhydride accelerated gum formation in fractions to which it was added. This was demonstrated experimentally. Iodine numbers were determined on the fractions before and after treating with maleic anhydride, and in all cases the iodine number of the treated material was found to be definitely lower than that of the control, the difference varying from 2 to 9 iodine numbers. As it is probable that this decrease in iodine number is not a quantitative measure of the conjugated diolefin content of the fraction, the figures are not given. This lowering in iodine number is, however, a
April, 1933
INDUSTRIAL AND EKGINEEKING CHEMISTRY
qualitative indication that some unsaturated materials \yere removed by the treatment; and, as maleic anhydride appears to be a specific reagent for the conjugated diolefins, the decrease in iodine numbers is probably due to the removal of these compounds. The almost complete stabilization a t 38" C. of these originally highly unstable fractions by treatment with maleic anhydride is a striking indication that conjugated diolefins are largely responsible for the initiation of gum formation. It can therefore be suggested that the primary reason for the occurrence of high peaks in the gum curves (Figure 3) lies in the occurrence in these fractions of appreciable concentrations of conjugated diolefins. That the fractions are not rendered permanently stable by treating with maleic anhydride is shown by the fact that they all form considerable amounts of gum when oxidized a t 50" C. (Table 11). This observation can readily be explained because any unstable hydrocarbons other than conjugated diolefins would still be present. These latter are apparently not as reactive as the conjugated diolefins and combine with oxygen a t a slower rate. The evidence here presented leads to the belief that the conjugated diolefins are the first constituents in the gasoline to start oxidizing and thus catalyze the oxidation of the otherwise relatively stable hydrocarbons (olefins in general), which, in turn, contribute their part to the actual amount of gum formed.
EFFECTO F SULFURIC ACID TREAThlENT ON GUM FORMATION In practice, cracked distillates are stabilized by treating with sulfuric acid. The small amount of acid that is used t o refine a cracked gasoline, and the fact that, in :I great many cases, 85 t o 90 per cent sulfuric acid will bring about the desired change, have led Brooks and Humphrey (6) to conclude that gum formation is initiated by the diolefins, because only the most reactive constituents would respond to such treatment. T'apor-phase cracked gasolines cannot be completely stabilized by treating with sulfuric acid, even when sufficient acid is used to cause rather large volume losses. Why this should be the case has not been satisfactorily answered. It was thought advisable, therefore, to treat the vapor-phase distillate with sulfuric acid, fractionate the treated material into a series of 5.6" C. (10" F.) fractions, and test the stability of these fractions. In carrying out this experiment, a quantity of the vapor-phase distillate was treated with concentrated sulfuric acid (equivalent to 6 pounds of acid per barrel of liquid) for 30 minutes with vigorous stirring. The sludge was removed, and the liquid was washed with successive portions of water, 10 per cent sodium hydroxide, and water, after which it was fractionated into series of 5.6" C. (10' F.) cuts. Seventeen fractions corresponding to the gum-forming fractions of the untreated material were tested for stability at 38' and 50" C. by oxidizing them for one week under 1.4 kg. per sq. cm. oxygen pressure and weighing the gum formed.
385
which involves shaking at room temperature, was followed. No preliminary purification of the fractions was ap lied. In a few cases (fractions 14 to 16 and the whole gasolinefthe hydrogenation was also carried on at 60' C. in an attempt to drive the addition more nearly to completion. The time allowed was 3 hours in all cases. The reaction was followed by the pressure in the system and the extent of hydrogenation by the iodine numbers of the products. The pressure drop indicated that addition of hydrogen proceeded rapidly, constant pressure being attained within 20 minutes a t room temperature and within 10 minutes a t 60" C. I n spite of this difference in velocity, the net result seemed to be that the hydrogenation reached a certain point independent of the temperature a t which it was carried on. This fact is made plain from the comparison of iodine numbers (Johansen method, corrected for substitution) given in Table 111. The whole gasoline offered an exception, reaching an iodine number of 30 a t room temperature and of 21 a t 60" C. XUMBERS OF FRACTIO~S OF VAPORTABLE 111. IODIXE PH.4sE DISTILL.4TE BEFORE ASD AFTER HYDROOENATION IODINE NEhfBER
7 -
FR.ACTIONBOILINQPOIST
c.
9 10 11 12 13 14 15 16 17 18 19 20 21 22
Whole distillateQ
68.3- 73.9 73.9- 79.4 79.4- 85.0 85.0- 90.6 90.6- 9 6 . 1 96.1-101.7 101.7-107.2 107.2-112.8 112.%118.3 118.3-123.9 123.9-129.4 129.4-135.0 135.0-140.6 140.6-146.1
..... , . .
a 29.4 t o 201.7'
,
After hydro- Biter hydroBefore hydro- genation a t genation a t genation 22-28' C. 60' C.
..
116.8 119.2 117.2 98.3 90.8 77.3 72.2 17.3 70.9 69.1 52.0 49.0 46.8 47.7
31.4 30.8 16.8 12.0 16.3 23.9 28.3 25.1 21.7 18.8 20.9 17.3 17.3 15.8
24:5 28.8 27.2
67.1
30.0
21.0
.. ..
C.
It is evident that there are certain constituents in the fractions and in the whole gasoline which hydrogenate readily, and that a considerable decrease in total unsaturation can be effected in this way. The hydrogenated materials (fractions 9 to 22 and the whole gasoline) were then submitted to oxidation tests, following the procediire described above, a t both 38" and 50" C. At the lower temperature all the fractions and the gasoline were entirely stable, forming no weighable amount of gum. At 50" C. the whole gasoline and fractions 10, 12, and 22 were quite stable; the rest formed gum more or less regularly, rising to a peak a t fraction 15 (Table 11).
COSCLVSIONS It is probable that hydrogenation will convert, in one way or another, all diolefins, conjugated or unconjugated, either to saturated compounds or to less reactive simple olefins; in None of these fractions gave gum in the 38" .:1( test. The addition, appreciable proportions of olefins are converted to data from the 50" C. test are presented in Table 11,and it is saturated compounds. IlIaleic anhydride will presumably evident that all the fractions tested are moderately unstable remove only conjugated diolefins. Sulfuric acid will almost a t this temperature. The failure to achieve commercial certainly remove the conjugated diolefins, probably the stability of vapor-phase gasoline by ordinary sulfuric acid unconjugated ones, and will to a slight extent attack the oletreatment can thus be readily understood. fins and aromatics. All three treatments render the fractions stable to oxidation a t 38" C. under the conditions of the test. EFFECTO F HYDROGENdTION ON GUM FORMATION These treatments also leave in the gasoline, compounds oxidizAs another means of connecting the gum-forming tendency able under more severe conditions. The ease with which the subsequent oxidation will occur with the unsaturated nature of the gasoline fractions, some may be expected to vary with the type of treatment by work on catalytic hydrogenation was undertaken. which the diolefins have been removed. This expectation is The reaction was carried out on fourteen fractions (9 to 22, inclusive) covering the gum-forming range of the unrefined mate- based upon the conclusion that the change of composition rial; 10-cc. samples of liquid with 0.05 gram each of Pt02.H20 effected by sulfuric acid and, still more so, that brought about as catalyst were used; the method of .4dams and Voorhees ( I ) , by hydrogenation will be more extensive than the simple
::(
INDUSTRIAL AND ENGINEERING CHEMISTRY
combination between maleic anhydride and conjugated diolefins, which presumably leaves the rest of the hydrocarbons quite untouched. As a matter of fact, the gum numbers obtained a t 50' C. show that the material treated with maleic anhydride is the most unstable, that in general the product treated with sulfuric acid follows, and that the hydrogenated fractions with a few exceptions are the most resistant to oxidation. This order of stability suggests that the constituents oxidizable a t 50" C. remaining after maleic anhydride or sulfuric acid treatment are olefinic in character. The susceptibility to oxidation of cyclohexene, as compared with simple olefins, cited above, suggests that the comparative stability of the hydrogenated products is due to more complete removal of cyclic olefins. The tentative conclusion to which this work leads seems to be as follows: The rapid deterioration of untreated highly cracked gasoline under the conditions of ordinary storage is dependent on the presence of conjugated diolefins. Following the suggestions of previous investigators, it appears that these diolefins go over to peroxides which may catalyze the further oxidation to gum of other relatively more stable unsaturated compounds. Mild treatment will remove these initiators of oxidation, and the residual products are somewhat more stable. These remaining unsaturated hydrocarbons, however, in time, or under more severe conditions, can be oxidized and will form gum, the tendency increasing with the concentration of the components. I n view of this conclusion it does not seem likely that highly cracked gasolines can be completely stabilized by treatments which remove only small proportions of unsaturated constituents, such as the di-
Vol. 25, No. 4
olefins, leaving the bulk of the unsaturated hydrocarbons unchanged. LITERATURE CITED
(13) (14) (15) (16) (17) (18) (19) (20) (21)
Adams, "Organic Syntheses," 1'01. VIII, p. 10, Wiley, 1928. Anonymous, Bur. Mines, Tech. Paper 323-A, 46 (1924). I b i d . , 323-A, 81 (1924). Ibid., 323-A, 86 (1924). Birch and Scott, IND.ENG.CHEM.,24, 50 (1932). Brooks and Humphrey, J. Am. Chem. Soc., 40, 852 (1918). Cassar, ISD.ENG. CHEM., 23, 1134 (1931). Chavanne, Am. Petroleum Inst., Rept. on Research in Petroleum, p. 27, June, 1932. Cooke, Bur. Mines, Rept. Inoestigations 2686 (1925). Diels and Adler, Ann., 460, 98 (1928). Egloff, Faragher, and Morrell, Am. Petroleum Inst. Proc. f 0th Ann. M e e t i n g , 11, No. 1, Sect. 111, 112-17 (1930). Flood, Hladky, and Edgar. PaDer oresented before Division of Petroleum Chemistry, 80th Meeting of American Chemical Society, Cincinnati, Ohio, Sept. 8 t o 12, 1930. Johansen, J. IND.EXG. CHEM., 14, 288 (1922). Kester and Andrews, Ibid., Anal. Ed., 3, 373 (1931). Kogermann, Trans. 2nd World Power Conferancc, Ecrlzn, 8, 33-42 (1930). Mardles and hloss, J . Inst. Petroleum Tech., 15, CJGb (1929). Peters and Baker, IND.ESG. CHEM.,18, 69 (1926). Rue and Espach, Bur. of Mines, Bull. 333, 68 (1930). Stevens, J . Am. Chem. Soc., 50, 568 (1928). Voorhees and Eisinger, J . Soc. Automotiae En0 , 24, 590 (1929). Zelinskii and Borisor, J . Russ. Phys. Chem. Soc., 62, 2051-4 (1930).
RECEIVEDOctober 13, 1932. Contribution 257 of t h e Department of Chemistry, University of Pittsburgh. This paper is a n abstract of a thesis presented t o t h e Graduate School of the University of Pittsburgh b y S. M , Martin, Jr., in partial fulfilment of t h e requirements for the P h . D . degree.
Cracking Alaskan Fur-Seal Oil GUSTAVEGLOFF AND E. F. NELSON, Universal Oil Products Company, Chicago, Ill.
F
CR-SEAL oil, extracted from the bodies of seals killed for their skins, is available in territoiy belonging to the United States, a fact that furthers interest in its properties and possible uses. It has been found that fur-seal oil cracks into high yields of gasoline of excellent knock rating. with fuel oil, fuel gas, or asphalt as by-products. Were the oil available in sufficiently large amounts, wc could propel our motor cars with seal gasoline over seal asphalt roads. Although the Pribilof Islands off the coast of Alaska are the breeding grounds of 80 per cent of the fur seals of the world, and sealing has been practiced there ever since the islands were discovered by the Russians in 1786, no more than 9000 gallons of fur-seal oil has been produced on the islands in any one year. The largest of the five islands of the Pribilof group is St. Paul where the seal by-product industry, as well as sealing activities, are centered, A new by-products plant was built there in 1930-31, which, according to a description published by the Bureau of Fisheries ( I ) , has a capacity of about 40,000 pounds of seal carcasses per 8-hour day. The type of reduction is known as dry-rendering. By this method, chopped seal carcasses are cooked and dried in one operation and the fat which is freed from the flesh tissue is removed from the dried material in high-pressure extraction equipment. PROPERTIES OF SEAL OIL Seal oil, obtained fiom the blubber of the animal, varies in color with the length of time which elapses between the killing of the seal and t,he extraction of the oil-i. e., the fresher the
tissue, the lighter the oil. A similar color gradation is noted with increasing temperatures of extraction, the higher temperatures producing dark oils. Commercial grades of seal oil are designated by color- white, straw, yellow, and brown. Most crude seal oils deposit stearin on standing. The amounts of free fatty acid and unsaponifiable matter vary, as may be seen from the data in the following table (3): F R E EF A T T T A C I D AS
SEALOIL
OLEICACID
% Kater-white Pale Cold-drawn pale Steamed pale Tinged (broan) NJnrwecian _D
Northern Very pale Yellow Light brown D a r k brown
0.2 0.0-1.5 1.80 1.46 8.29 7.33 3.2 0.98-1.13 1.41 4.09 19.95
UXSaPOXI-
FI.4BLE
MATTER
OBSERVER
% 0:5 0.38 0.43 0.51 1.05
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Lewkowitsch Lewkowitsch Thomson and Ballantyne Thomson a n d Ballantyne Thomson and Ballantyne Thomson and B a l l a n t w e Bull Chapman a n d Rolfe Chapman and Rolfe Chapman and Rolfe
First-quality seal oils are used as buriiing oil in lighthouses, and, sometimes, as an adulterant of cod liver oil. The latter use is possible because the composition of seal oil approximates that of cod liver oil, with even less taste and smell. The lower quality seal oils find use in soap making, especially in the manufacture of soft soaps, and in the leather industries. Seal oils that have been blown with air are useful, t o some extent, as lubricating oils in admixture with other oils. Although they hare high specific gravity and viscosity, blown seal oils tend to gum and have low flash points. The changes wrought in seal oil by blowing with air are as follows:
