INDUSTRIAL AND ENGINEERING CHEMISTRY
1132
Vol. 23, No. 10
Gumming Tendencies of Pure Olefins in Gasoline' Harold A. Cassar TECHNICAL
SERVICEDIVISION,STANDARD OIL COMPANY OF NEW JERSEY, ELIZABBTH, N. J.
Simple olefins in 20 per cent concentrations do not produce gum even after oxidation a t 100" C. and 100pound (45.4-kg.) air pressure for 4 hours, which conditions cause most cracked gasolines to produce quantities of gum. Simple olefins begin to produce gum in 20 per cent concentrations after 24-hour oxidation ; diolefins in 20 per cent concentrations give large quantities of gum under simple evaporation. Sulfuric acid partly transforms olefins into gummy substances, nonvolatile in steam. Sulfur dioxide contacted with olefins for short periods of time, even if followed by a caustic wash, produces gum. This is because of the oxidation of sulfur dioxide to very reactive sulfur trioxide by the peroxides in the olefins. An olefin free from peroxides does not give gum with sulfur dioxide. Olefin peroxides catalyze the formation of gum in un-
stable stocks; diolefins do not catalyze the formation of gum if they are free from peroxides. Caustic soda, hydrogen chloride, hydrogen sulfide, acetic acid, and free sulfonic acids do not change olefin peroxides into gum. A caustic wash restores the inhibition period of an olefin to its original length of time after it has been cut down by oxidation. A caustic wash improves the porcelain-dish gum of an aged gasoline t h a t gives a positive reaction for peroxides: if the peroxide reaction is negative, the caustic wash may improve the gum, or may make it worse. Olefin peroxides are strong knock inducers; they are readily destroyed by caustic soda or by formaldehyde and should not be present in pure olefins whose knock ratings are being determined for purposes of standardization. The gum content of gasoline fractions bears no direct relationship to either boiling point or sulfur content.
. .. . .
T
HE object of the work described in this paper was to study the gumming tendency of pure olefins dissolved in a highly refined gasoline, and, if possible, to determine
why cracked gasolines from the same gas oil and made by different processes vary in stability as regards gum formation. It has been fairly well established that the initial step in gum formation involves the absorption of oxygen to form substances commonly referred to as peroxides; the subsequent steps leading to gum, either directly or through the aldehyde or ketone stage, are not completely understood at present. The following olefins representative of straight and branched-chain aliphatic, cyclic, diolefinic, and unsaturated aromatic hydrocarbons were prepared synthetically or by dehydration of alcohols: 2-pentene, trimethylethylene, hexene, heptene, diisobutene, diamylene, cyclohexene, dimethylbutadiene, 2-methylhexadiene, 2,4-limonene, and styrene. These olefins, with the exception of limonene which was vacuum-distilled, were distilled over sodium immediately before using to insure their freedom from peroxides. The experimental procedure adopted in general was to blend the various olefins in definite proportions with an olefin-free gasoline and then determine the porcelain-dish gum and the accelerated gum. The porcelain-dish gum was determined by evaporating 100 cc. of the blend in a 4-inch (10.2-cm.) porcelain evaporating dish on an actively boiling water bath provided with hood and ventilating fan; the accelerated gum was determined by heating the blend for 4 hours in bombs under 100-pound (45.4-kg.) air pressure in a steam-heated bath and then taking the porcelain-dish gum on the resulting oxidized product. The bombs used were described in a previous paper by Cassar ( I ) and this design, coupled with pressure-recording gages, etc. (S), is becoming standard in the company. The olefin-free stock is straight run gasoline treated with AIC1, to remove unsaturates and steam-distilled, Aromatics are present, although modified by the Friedel and Craft reactions, and 2 4 hour acceleration gives 1 to 2 mg. of gum. Gums from Olefins and Diolefins in 20 Per Cent Blends The experiments summarized in Table I show that 4-hour acceleration, which causes most gasolines to gum consider1
Received June 23, 1931.
ably, does not affect simple olefins but only diolefins in 20 per cent blends. Acceleration for 24 hours causes simple olefins in 20 per cent blends to gum, however. One interesting conclusion is the possibility of preparing a gasoline rich in aromatics and olefins and, therefore, with a high antiknock rating that is quite stable with respect to gum. Gums of 20 P e r C e n t Blends of Ole6ns in Olefin-Free S t o c k PORCELAIN-DISH GVM No 4-hour 24-hour accelera- accelera- acceleraSAMPLE tion tion tion Mg./ Mg.l Mg./ 100 cc. IOG cc. 100 cc. nlefin-frer 0 0 1 I._._I.. stock Olefin-free stock and 20% 2-pentene 0 6 38 Olefin-free stock and 20% trimethylethylene 0 1 35 Olefin-free stock and 20% cyclohexene 0 0 45 Olefin-free stock and 2 0 7 hexene 1 2 .. Olefin-free stock and 20% heptene 1 1.5 Olefin-free stock and 20% diisobutene 0 1 .. Olefin-free stock and 2 0 7 diamylene 0 1 .. Olefin-free stock and 20.3 dimethylbutadjene 70 .. .. Olefin-free stock and 20% 2-methylhexadlene 2 Olefin-free stock and 20% limonene 8 230a a Acceleration of 1.5 hours T a b l e I-Porcelain-Dish
__
..
....
Effect of Treating Olefins
SULFURICAciD-Olefins in 20 per cent blends were treated with concentrated sulfuric acid (66 BaumP) in quantities corresponding to 6 pounds per barrel (7.5 cc. per liter) and agitated for 15 minutes, the sludge was drawn off, and the blend water and caustic washed. As can be seen in Table I1 the olefins, when acid-treated, are not completely removed as sludge, but some of them remain in the gasoline as high-boiling and very sticky polymerized substances which are not volatile in steam. The behavior of 2-pentene is abnormal. T a b l e 11-Gum
in Olefine a f t e r Acid T r e a t m e n t PORCELAIN-DISH GUM Acid treatment and SAMPLE (ZOOJ, BLENDIN OLEFIN- Acid treatment steam distillation FREESTOCK) Mg./lOO cc. Mg./100 cc. 148 2-Pentene 773 2 Trimethylethylene 181 20 Diamylene 26 Diisobutene 5 1,039 Cyclohexene 2 Styrene 14,786 (clear yellow sirup)
... ...
INDUSTRIAL AND ENGINEERING CHEMISTRY
October, 1931
.
SULFURDIOXIDES-olefins in 20 per cent blends produce gum in the presence of sulfur dioxide. The experiments summarized in Table I11 show that in every case examined, sulfur dioxide increases the gum content of those olefins that contain peroxides, while it has little effect on pure olefins, free from peroxides. Caustic soda also destroys the peroxides and thus renders the olefins almost as immune to attack as they were before oxidation. The concentration of sulfur dioxide used was 3 grams per liter; time of acceleration to form peroxides, 4 hours; and strength of caustic, 10 per cent. The sulfur dioxide was added to the blends after accelerating and just before evaporating in porcelain dishes. A caustic wash after the peroxides come in contact with sulfur dioxide is of no use. It is, therefore, important to keep gasolines alkaline or, a t least, peroxide-free in the sulfur dioxide atmosphere of a refmery. Peroxides were shown to oxidize sulfur dioxide to the very active sulfur trioxide by shaking an olefin, containing peroxides, first with sulfur dioxide and then with barium hydroxide to give a white precipitate, partly insoluble in hydrochloric acid, owing to the barium sulfate. The perosidefree olefin treated successfully with sulfur dioxide and with barium hydroxide gave a precipitate completely soluble in hydrochloric acid. T a b l e 111-Gum
in Olefins w i t h S u l f u r Dioxide S h o w i n g Effect of Peroxides ___-____--GUM FORMED Peroxidized,
__---_--
OLEFIN(Z070 BLENDIN OLEFINFREESTOCK) Cyclohexene Trimethylethylene Hexene
Peroxidefree SO? treated Mg./ 100 cc. 17 1.5 3 A
Peroxidized
Mg./ 100 cc. 0
3 3 n
Peroxidized, SO? treated Mg./ 100 cc.
287
53 114
Pen1
Peroxidized, caustic washed, SO1 treated Mg./ 100 cc. 4 11 7 6
9
..
SO? treated, caustic washed after 15 minutes Mg./ 100 cc. 7 16
.. ..
1133
difference of pure limonene in raising the gum of the unstable gasoline used from 18 to 36, while the peroxidized limonene raised the gum from 161 to 302; hence, the catalytic effect of diolefins, when present, is due to peroxides and not to the diolefins as such. T a b l e V-Catalytic
Effect of Diolefins D u e to Peroxides PORCELAIN-DISH SAMPLE GUM Mg./100 cc.
7 0 7 olefin-free stock, 30% unstable gasoline
60% olefin-free stock, 30% unstable gasoline, 10% pure limonene 60% olefin-free stock, 30% unstable gasoline, 10% peroxidized limonene 90% olefin-free stock, 10% peroxidized limonene
18 36
302 161
Effect of Caustic Soda on Peroxides
Peroxides are known to decompose to form aldehydes and acids in contact with water and, since aldehydes are readily polymerized by means of alkali, it was thought probable that decomposing the peroxides with caustic soda would yield gums. Such, however, was not found to be the case with the olefms examined in Table VI. The S. K. I. reaction mentioned in this table is taken by shaking a gasoline or blend with an equal volume of starch-potassium iodide solution (5 per cent KI); if a blue color develops within a minute, the S. K. I. reaction is said to be positive and is usually a sign of the presence of peroxides in the unsaturates. T a b l e VI-Effect of C a u s t i c Soda on Peroxides PORCELAIN DISH-GUM HYDROCARBON (20% AFTER 4-HOUR S. K. I. RSACTION BLENDI N OLEFINOXIDATION AND Before After FREESTOCK) CAUSTIC WASH wash wash M g . / 1 0 0 CC. Diamylene Pentene-2 Trimethylethylene Cyclohexene Diisobutene Hexene
12 3
..
Effect of Peroxides on Stable and Unstable Gasolines
Three experiments were described by the National Renzole Association of Great Britain ( d ) , where peroxides, made from barium peroxide and acetic anhydride, were added to unrefined benzenes and produced gum only with unstable samples of benzene. This has been checked with petroleum distillates, the peroxides being prepared by oxidizing olefins in bombs; an unstable vapor-phase cracked stock was shown to be markedly affected by peroxides, while a relatively stable liquid-phase cracked stock was much more resistant, as shown in Table IV. of Peroxides on S t a b l e a n d U n s t a b l e G a s o l i n e s ------GUM FORMED ------2TriCycloSAMPLE Diamylene Pentene methylene hexene ME./ ME./ Mg./ ME./
Rejuvenation of Peroxidized Olefins
To bring out in a rather more definite way the fact that caustic soda solutions act as rejuvenating agents on peroxidized olefins, 200 cc. of a 50 per cent blend of cyclohexene and olefin-free stock were put into an oxygen bomb with recording gage for 2 hours, and the contents were then divided into two parts. The pressure on the 200-cc. sample held up for 75 minutes the inhibition or induction period. One of these parts was reheated in the oxygen bomb while the other was washed with caustic soda before reheating. The first portlion held up for 45 minutes while the second caustic-washed sample stood up for 75 minutes before the pressure started to drop. This latter period is the same as that of the original cyclohexene blend before oxidation.
T a b l e IV-Effect
100 cc.
+
Stable 20% uure olefin Stable 20% bxidized-Aefin Unstable ZOy0 pure olefin Unstable 20% oxidized olefin
++ +
5
18 135 735
100 cc.
100 cc.
in
R
8 156 260
79 321
-.
14
100 cc. 7 10
179 683
Catalytic Effect of Diolefins Due to Peroxides
A small proportion of a readily oxidizable hydrocarbon in a cracked gasoline which is unstable has been said to cause the resinification of a relatively large proportion of other constituents of the unstable gasoline in the usual gum-evaporation test ( 5 ) . The experiments summarized in Table V show the in-
Catalysis of Olefin-Peroxide Gumming
Since peroxidized o l e h s are gradually changed into gums, and aged gasolines exhibit an acid reaction, it was thought possible that the hydrogen ion might change peroxides into gum. This belief was substantiated by the reports of Wagner (7) who worked with HCI and acetic acids; of Smith (5) who said, “The antioxidant, being basic, combines with the acidic products of oxidation and prevents them from acting as autocatalysts towards oxidation;” and of Stadnikov (6) on transformer oils and free sulfonic acids. It was found, however, that acids do not change the peroxides of simple olefins into gums, a t least in the cases investigated. To test this matter, six olefins were oxidized for 4 hours and then made into 20 per cent blends with olefin-free
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
1134
stock which had previously been treated with the requisite quantities of acetic acid, hydrogen chloride gas, and hydrogen sulfide gas so that the resulting blends would be 0.1 N in strength. Ten milligrams of oil-soluble free sulfonic acids from Penivian stock were added to the fourth series. Table VI1 shows that there is very little catalytic action since scarcely any resins were obtained. Table VII-Negative SAMPLE Hexene Cyclohexene Diisobutene Trimet h) lethylene 2-Pentene Diamylene
Effect of Some Acids on Peroxides PORCELAIN-DISH GUM-Acetic acid HtS HC1 Sulfonic acids ME./ Mg./ AMs./ Lug./ 100 cc. 100 CC. 100 cc. 100 cc. 2 2 2 3 3 3 3 2 3 12 6.5 2 1 1 12 1 1 1 1 1 4 10
Effect of Caustic Soda Wash on Aged Gasolines
It was found that in certain cases a caustic wash would improve the gum content of a gasoline, while in other cases it would have the opposite effect. This was rather baffling and was put down to the character of the crude from which the gasoline originated, which was begging the issue. Further work showed that a caustic wash would improve the gum content of an aged gasoline if the gasoline exhibited a positive S.K.I. reaction; if the aged gasoline exhibited a negative S.K.I. reaction, a caustic wash would either not affect the gum content or make it worse, as is well borne out by the figures of Table VIII. T a b l e VIII-Effect
of Caustic Soda Wash on Aged Gasolines
In this connection it might be well to paint out that investigators reporting knock ratings of pure olefins could, advantageously, state whether they redistilled their olefins over sodium immediately before their knock ratings were determined. (In the system on knock ratings in vogue at the present time, a knock rating of 0 corresponds to a .50 per cent blend of benzene in standard-knock gasoline; a knock rating of 5 corresponds to a 30 per cent blend of benzene in standard-knock gasoline; and a knock rating of 10 corresponds to straight-run Midcontinent gasoline.) Gum Distribution in Gasolines
A vapor-phase cracked stock was fractionated into 10 per cent cuts; each cut was then oxidized separately for 4 hours and its gum content determined. A sulfur determination was run at the same time. It was found that the gum content was not proportional to the boiling point of the fractions analyzed and did not bear any direct relationship to the total sulfur content of the cut. Distribution i n Vapor-Phase Cracked-Stock 10 Per Cent Cuts cut 1 2 3 4 5 6 7 8 9 Sulfur, k 0 . 0 1 9 0 . 0 3 6 0 . 0 5 9 0.086 0 . 1 1 4 0 . 1 3 7 0 . 1 6 8 0 . 1 8 2 0.220 Gum (bomb, 4 h o u r s ), mg./lOOcc. 240 523 1082 938 785 424 495 436 179 Table X-Gum
Acknowledgment
Grateful acknowledgments are extended to H. G. Schneider for his valuable advice and to H. E. Buc who donated all the aliphatic olefins used, with the exception of diamylene.
PORCELAIN-DISH GUM GASOLINE S. K. I. REACTION Original After caustic wash Mg./lOO cc. .Mg./IOO Cc.
Effect of Peroxides on Knock Rating
Callendar was one of the first to show the production of peroxides in an engine. To determine the effect of peroxides on knock rating, three olefins were distilled over sodium and made into 30 per cent blends with standard-knock gas (knock rating of 10). These are the “no peroxide” blends in Table IX. Samples of the olefins were oxidized for 4 hours under standard conditions [looo C. and 100 pounds (45.4 kg.) oxygen] and, when blended, constitute the peroxide blends in the table. One portion of these oxidized blends was agitated with 5 per cent caustic soda solutions and another with formaldehyde solutions to destroy peroxides. The results, as shown in the table, prove that peroxides are very efficient knock inducers and are destroyed by caustic soda or formaldehyde solutions ( 2 ) . Table IX-Effect
Literature Cited (1) Cassar, IND. ENG. CHEX.,.4nal. Ed., 3, 197 (1931). (2) Egloff, Faragher, and Morrell, Refiner Natural Gasoline M f r . , 9, 1, 80 (1930). (3) Hunn, Fisher, and Blackwood, J . Soc. Aufomotive Eng., 26, 31 (1930). (4) Joint Benzole Research Committee, Nat. Benzole Assocn. and Univ Leeds, Great Britain, R e p f s . 4-7 [Rept. 7 reviewed in Gas. J . 191, 37 (July, 1930)). (5) Smith and Wood, IND. EHG.CHEM.,18, 691 (1926). (6) Stadnikov and Vozzhinska, Perroleurn Z.,25, 651 (1929). (7) Wagner and Hyman, J . I n s f . Pelroleum Tech., 15, 674 (1029).
Bibliography
of Peroxides on K n o c k R a t i n g KNOCK S. K. I.
2-PENTENE, 10 No peroxide Peroxide Peroxide and caustic
30 PER C E N T
PER CENT
RATING REACTION STANDARD-KNOCK GASOLINE 4.6 8.3 5,0
-
+-
30 PER CENT CYCLOHEXENE, 10 PER CENT STANDARD-KNOCK GASOLINE
No peroxide Peroxide Peroxide and caustic Peroxide and formaldehyde
-
6.0 12.0plus 6.3 7.0 SO PER CENT DIAMYLENE, 70 PER CENT STANDARD-KNOCK GASOLINE 3.8 No peroxide 5.8 Peroxide 5.0 Peroxide and caustic 5.4 Peroxide and formaldehyde
+ -
+ -
Vol. 23, No. 10
(23) (24)
(25) (26) (27) (28) (29)
Auld, J . Inst. Petroleum Tech., 15, 645 (1929). Bailey, J . SOL.Chem. Ind., 48, 2, 35 (1929). Bridgeman and Aldrich. J . SOL.Automotioe Eng., 28, 2, 191 (1931). Brooks, IND. ENG. CHEM.,18, 1200 (1926). Brooks and Humphrey, J . A m . Chem. Soc., 40, 822 (1918). Brooks and Parker, I N D . EHG.CHEM.,16, 587 (1924). Bureau Mines, Tech. Paper 323-B. 96 (1927). Cooke, Bur. Mines, R e p f s . Inoestigations 2686 (1926). Dean, Bur. Mines, Tech. Paper 214 (1919). Engler, E e r . , 33, 1090 (1900). Flood, Hladsky, and Edgar, Oil Gas J., 29, 18,40 (1930). Herthel and Apgar, A m . Petroleum I n s f . Bull., 11, 3, 124 (1930). Littlejohn, Thomas, and Blackwood, J . SOL. Automotiae Eng., 26, 31 (1930). Mardles and Moss, J . I n s t . Petroleum Tech., 15, 657 (1929). Milas, J . Phys. Chem., 33, 1204 (1929). Moureu, Ckimie industrie, Spec. No., 101-9 (1927). Moureu, I b i d . , 47, 829 (1928). Moureu and Dufraisse, Chem. Reuiews, 3, 113 (1927). Moureu. Dufraisse. and Badocke. Bull. SOC. chim.. 35, 1564 (1924). Naphthali, Chem.-Ztq., 54, 371 (1930). Norris and Thole, J . I n s f . Petroleum Tech., 15, 681 (1929). Rue and Espach, Oil Gas J . , 28, 42, 186 (1930). Smith and Cooke, Bur. Mines, Repts. Investigations 2344 (1922). Staudinger, Ber., 58, 1075 (1925). Stephens, J. A m . Chem. SOL,50, 568 (1928). Story, Provine, and Bennett, IND. ENG. CHEM.,21, 1079 (1929). Story and Snow, Ibid., 20, 359 (1928). Vilkas and O’Neill. Petroleum Eng., 1, 2, 82 (1929). Vorhees and Eisenger, Oil Gas J . , 27, 31, 152 (1928).
