1234
INDUSTRIAL AND ENGINEERING CHEMISTRY
(3) Cleveland and Fulweiler, Ibid., 61,749 (1928). (4) Dashiell, U.G.I. Circle, 11, No.7, 24 (1931). (5) Fdweiler, Jordan, and Ward, Am. Gas Assoc. Proc., 1927, 1418. (6) Lence, Gus- u. Vusserfach, 74, 1169 (1931); Rettemsier, Ibid., 75,541 (1932). (7) Menery, Am. Gus Assoc. Proc., 1931, 1082.
VOl. 25, KO.11
(8) Powell, Merritt, and Byme, Gas Age-Record, 60,3 (1927); Kohr,
Ibid., 57, 187 (1926). (9) Ward, Jordan, and Fulweiler, ISD. ENG.CEBM.,24, 969, 1238 (1932). R ~ C E I V BJune I D 3, 1933.
Chemical Nature of Gum-Forming Constituents in Gasoline DONALT. FLOOD, J. W. HLADKY, AND GRAHAM EDGAR, Ethyl Gasoline Corporation, Detroit, Mich.
W
I T H the progress of
t e n d e n c i e s . The results reThe problem of determining the source of gum the cracking industry, ported in this paper represent in gasoline has been attacked by a n investigation and particularly with a preliminary i n v e s t i g a t i o n of individual hydrocarbons of the type likely to the development of c r a c k i n g along such lines. processes designed especially to be formed by cracking processes. These were PREPARaTION O F MATERIALS improve the antiknock quality added in varying amounts to straight-run AND EXPERIMENTAL TECHNIC of gasoline, m a n y p r o b l e m s parafink gasoline and the mixtures subjected to have arisen connected with the GASOLINES. F o u r different the usual tests for gum stability as well as to instability of the products of gasolines were e m p 1o y e d for storage tests. B y f a r the largest amounts of c r a c k i n g . This instability is blending with the individual hygum observed were developed in those mixtures manifested particularly in the drocarbons. All were straighttendency of the cracked gasocontaining aliphatic or cyclic diolefins, or monorun paraffinic g a s o l i n e s , and line to develop objectionable were treated exhaustively with olefins attached to a benzene ring. I n certain amounts of gum on storage and sulfuric acid, washed with soda, cases: however, those containing large concenin the loss of antiknock value dried, and distilled. None of trations of aliphatic monoijlejns also formed on storage, with and without t h e m g a v e weighable gum or concurrent formation of gum. appreciable quantities of gum. Gum formation showed oxygen absorption under Many recent papers have disis almost invariably associated with oxidation. the conditions of test, and no cussed various a s p e c t s of the difference could be observed in The effectiveness of inhibitors is demonstrated problem, and, although the rethe results obtained when the and their action is shown to consist in a prolongsults of different investigators same hydrocarbon was blended ing of the induction period without apparently are not always in entire accord, with different gasolines. affecting the rate of oxygen absorption once the certain generalizations s e e m to HYDROCARBONS. All hydrobe reasonably well agreed upon: induction period is finished. A comparison of carbons were synthetic products. All were freshly distilled before storage test with oxygen bomb data indicates that (1) It is the gum actually present in gasoline at the time of its u s e (a p r e c a u t i o n essential no simple relation exists between the time of stause which gives trouble in autoin some cases), and a close disbility in storage and the length of the induction mobiles because of clogged fueltillation c u t w a s e m p l o y e d . i n d u c t i o n systems, stuck inlet period by the oxygen bomb. Nevertheless a Precautions w e r e t a k e n t o valves, etc. (18, 85). study of the complete oxygen bomb pressure curve (2) The tendency of a aeoline remove all k n o w n impurities t o form gum in storage is%est ind i f f e r i n g c o n s i d e r a b l y in may give valuable indications of the behavior of dicated by some form of oxidation nature from the hydrocarbons the mixture in storage. test (14, 18, 25). t h e m s e l v e s . I t is difficult (3) Gum formation is usually, if n o t i n v a r i a b l y , associated to exclude, however, in some with oxidation (3). cases the possible presence of isomers in which the double (4) Gum formation may be inhibited bv addinn to the easoline bond or bonds are in a different location from that of the main small amounts of various substances, usudly antyoxidanti (7). ( 5 ) Gasolines may lose antiknock value on storage, apparently portion, and in many cases cis-trans isomers were almost by formation of oxygenated compounds acting as knock inducers, certainly present. The formulas employed represent the or in some cases by actual removal, through gum formation, of most probable structures, and in most cases there is little hydrocarbons high in antiknock value, and the antiknock value may be partially or wholly restored by certain refinery treat- doubt that they represent a t least the major portion of the material used. ment (7). EVAPORATION TESTS. These tests in porcelain dishes Practically all of the published data have given the results were carried out on a steam bath on 50-ml. samples. Evaporaof experimental work on cracked gasolines whose chemical tion tests in glass were carried out on 50-ml. samples in glass constitution, a t least as far as individual hydrocarbons are beakers in an oven through which a current of superheated concerned, is quite obscure. It would appear, therefore, that steam was passed. The average oven temperature was a valuable line of attack on the problem of gum formation 160" C. Residues were in all cases evaporated to constant would be the investigation of individual hydrocarbons of weight. OXIDATION TESTS. These tests were carried out a t 100 the type likely to be formed by cracking processes, in order to determine if possible what types of hydrocarbons are pounds per square inch (7 kg. per sq. cm.) oxygen pressure responsible for gum formation in gasoline, and the behavior and 100" C. The apparatus was of conventional type (16). of such hydrocarbons when subjected to the various tests At the end of the period of heating (4 to 96 hours) the bomb which have been proposed as an indication of gum-forming was cooled to 20°, the pressure read, and a 50-ml. sample ~
November, 1933
TABLE I.
8 9 10 11 12 13
14 15 16 17 18 19 20 21 22 23
1-Heptene 1-Heptene 1-Octene 1-Octene 1-Octene 1-Octene 2-Octene (caprylene) 2-Octene (caprylene) 2-Octene (caprylene) 2-Ootene (caprylene)
24 25 26 27 28
4-Octene 4-Octene 4-Octene 4-Octene 4-Octene
123.8-124.5
29 30 31 32
Diisobutylene Diisobutylene Diisobutylene Diisobutylene
101.1-102.1
33 34 35
Cyclohexene Cyclohexene Cyclohexene
36 37
Methylene cyclohexane 100-103.5 3-Cyciohexyl-1-propylene (allylcyciohexane) 154.0-155.0
7-p
1 2
3
4 5
g I
-
MOKOOLEFISS
-OXYGEN EYAPN.Time InHTDROCARBOX , IN of ducBoiling In STEAM heattion Name range mixture OVEN ing period % by M o l e s / M g . / C. vol. liter 100 cc. Hours Hours 4 >4 3 2-Pentene (amylene) 10 0 . 9 3 35.7-36.8 4 3.5 2-Penteile (amylene) 20 2.75 4 23 2-Pentene (amylene) 1.5 4 33 2-Pentene (amylene) 4 1.5 38 2-Pentene (amylene) 1.25 4 46 2-Pentene (amylene) 4 1.0 67 2-Pentene (amvlene) Trimethylethylene 35.6-37.1 10 0 . 9 4 0 4 >4 Trimethylethylene 10 0.94 72 7.0 Trimethylethylene 20 1.89 4 2.0 Trimethylethylene 33 3.14 , 4 2.0 Tetramethylethylene 70.5-73.5 10 0.84 4 0.75 Tetramethylethylene 33 2.77 4 0.25
No.
1235
INDUSTRIAL AhD ENGINEERING CHEMISTRY
. . ..
BOMB
Pressure drop Lh./sq. in. (kg./sq. cm.) 0 (0) 5 (0.35) 5 (0.35) 35 (2.5) 35 (2.5) 40 ( 2 . 8 ) 55 (3.9) 0 (0)
......
35 40 55 75
(2.5) (2.8) (3.9) (5.3)
33 3.5 1.25
5 (0.95) 5 (0.30) 0 (0) 15 ( 1 . 1 ) 5 (0.35) 5 (0.35) 0 (0) 20 ( 1 . 4 ) 5 (0.35) 25 (1.8)
4 96 23 4 4
4 551 5.5 3.5
5 (0.35) 10 ( 0 . 7 ) 80 (5.6) 10 (0.7)
..
4 23 4 4
4 8 4 1.0
S(0.35) 45 ( 3 . 2 ) 5 (0.35) 30 (2.1)
0.99 2.96 3.95
0 3 ,
4 4 4
10
0.83
1
4
>4
10
0.66
4
4
4
145.2-147.6
10 33
0.86 2.88
101 ,
4 4
0.5 0.1
176-178.4
10
0.77
0
4
0.25
165.4-166.0
10 33 10 33
0.77 2.57 0.75 2.51
0
4 4 4 4
92.7-93.2 121.3-122.4
124-126
83.0
10 33 10 20 33 67 10 10 33 67
0.70 2.34 0.63 1.27 2.11 4.22 0.64 0.64 2.14 4.28
10 10 20 33 67
0.64 0.64 1.28 2.14 4.28
0
. ...
10 20 33 67
0.65 1.30 2.17 4.34
0
10 30 40
, . . .. .
..
0
.
.
96 4 4 23 4 4 4 96 4 4
801 4 >4 16 4 3.5
>?
.........
4
...
1.0
...... ......
......
Gum NOTESON by steam ,-~TOR.AGE TEST ( ~ ~ o N T H S:--) PREPAR.4TION oven Initial 4 8 12 16 20 24 Mg./ Milliarams/cuhic centimetera 100 cc. .. . . Refractiona3 15 17 3 0 0 .. tion of E a s t .. .. 21 .. man Kodak 14 product 10 8 171 70 91 .. 226 0 0 5 5 0 2 3 2 ( f 5 ) 507 . . . . . . . . . . 114 . . . . . . .. 82 . . . . . . . . . . . 166 0 0 0 21 75 . . (CHs)zCOHCH109 . . . . . . . . . . . . . hydrated (CHdr deby iodine (6) 34 . . . . . . . . . . . . . BuMgBr 9 . . . . . . . . . . . . . allyl bromide 6 24 . . . . . . AmMgBr 0 . . . . . . . . . . . allyl bromide 95 . . . . . . . 28 48 2 . . . . . . . . . . 13 0 0 0 . . . . . . . . . . Dehydration . . . . . . . . . . . . of 2-octanol 188 . . . . . . . . . . . (EastmanKo10 66 . . . . . . . . . . . . . dak) uaing p 105 tolueneaulfonic acid 3 0 .. 4 18 . . . . . . BuMgBr 160 . . . . . . . . . . . . CsHiCHO 355 . . . . . . . . . . . . . 4-octanol fol8 . . . 20 . . . . . . . . lowed by’ de98 . . . . . . . . . . . . . hydration usina p-toluenesdfonic acid 4 0 7 0 27 . . . . . . Refraotiona211 . . . . . . . . . . tion of prodg i ii 7 23 24 .I. .. uot from 108 6 5 12 8 15 . . Standard Oil Co. of New Jersey 0 0 0 0 8 15 27 .. Refractiona4 181 235 390 1080 tion of East18i 13 18 . . . . . . . . man Kodak
.
+ +
..
+ -+
.
. . . .
.
0 (0)
7
0
3
8
17
16
15
12
10 (0.7)
4
5
15
17
20
14
26
..
r::::) +.
CeHllMgBr allyl bromide refractive in: dex, 1.451 a t
200
38 Phenylethylene rene) 39 Phenylethylene 40
(sty-
1-Phenyl-1-propylene
41 2-Phenyl-1-propylene 42 2-Phenyl-1-propylene 43 3-Phenyl-1-propylene 44 3-Phenyl-1-propylene a
160.6-161.1
.
.
0
>4 1.0 4 1.5
......
0
7
36
55 (3.9)
461
0
20
38
48
0 (0) 20 (1.4)
3 58 3 441.f
0
10 55 0 37
6 40 5 1350
18
......
......
25 (1.8)
c.
.. R e f r a o t i o n a . . . . . . . . . . . . . tion of Eastman Kodak
3034+ 15425+
.
2
.
168 1823 5952
104 400
16
16
product 614 D e h y d r . a t i p n using iodine catalyst (18,
. . . . . . . .
26
(83) 17)
.6 . .18. .42. .250.
(84)
On evaporation in porcelain dish.
of the gasoline evaporated on the steam bath as above, any separated gum being dissolved in acetone-benzene and estimated separately. I n estimating induction periods, 15 minutes were deducted from the time to allow the bomb to come approximately to the temperature of the bath. The difference between the initial pressure and the final pressure after cooling is called “pressure drop,” and is probably an approximate measure of the oxygen consumed in the reaction. I n some cases the induction period is so short that an accurate estimate of it is impossible and, in cases where any figures given are less than 0.5 hour, must be taken with some reservation. I n certain other cases, where the induction period is very long and the rate of pressure drop very slow, it is likewise difficult to estimate the induction period with any accuracy. In some of the earlier experiments the bombs were not cooled to the identical temperature a t which they were filled, and the pressure drop recorded may be somewhat in error by virtue of temperature variations.
AGING TESTS. Blends were stored in half-gallon (1.9liter) cans a t room temperature. The cans were only partly filled so that considerable air was always present. At the end of 4 months a sample was withdrawn and evaporated in a porcelain dish. If gum had separated from the mixture, the blend was removed from the can, the gum dissolved out and determined by evaporation, and the amount corresponding to the sample evaporated was calculated and added to that found in the sample itself. The blend was then returned t o a clean can for further storage. All tests were not run on every sample, partly because of the limited quantity of hydrocarbon available, and partly because during the investigation the original plans were somewhat modified in the light of preliminary experimental results.
REHJLTSOF TESTS The experimental data are recorded in Tables I to IV and in Figures 1 to 5. Certain general conclusions may be drawn. It should be emphasized that these conclusions refer only to.
1236
INDUSTRIAL AND ENGINEERING CHEMISTRY
the data in question; how g e n e r a l l y they may be applicable is a m a t t e r for f u r t h e r experimentation. With two exceptions (noted below) none of the fresh blends gives a weighable amount of gum when evaporated in p o r c e l a i n or glass (steam). In the o x i d a t i o n t e s t s , gum formation is invariably associated with oxygen absowtion ( p r e s s u r e drop). In no case was an appreciable a m o u n t of gum formed where no pressure drop o c c u r r e d . Slight pressure drops were occasionally observed w i t h o u t t h e formation of weighable gum, but any appreciable drop in pressure was always associated with some gum formation. No general correlation could be observed for different hydrocarbons between t h e amount of p r e s s u r e drop and the gum f o r m e d (compare experiments 11 and 30, Table I, with experiments 45, 61, and 66, Table 11). The pressure begins to fall after an induction p e r i o d d u r i n g which the pressure remains essentially constant. The rate of fall of p r e s s u r e after the induction period is (for individual hydrocarbon blends in the absence of an inhibitor) greater, the shorter the induction period (Figure 3). All hydrocarbons reported will show pressure d r o p a n d g u m formation if h e a t e d FIGURE 1. MONO~LEFINS AND MIXTURESOF OLEFINS sufficiently 1on g , but the l e n g t h of the induction period varies greatly (compare experiment 9 with 25). ALIPHATICMONOOLEFINS. None of the monoolefins shows gum formation or appreciable pressure drop in concentrations of 10 per cent by volume at the end of 4 hours of heating. After much longer periods of heating, however, all of them show gum a t this concentration (experiments 9 14,21, and 25, and Figure 5). With increasing concentration the induction period is
Vol. 25, No. 11
decreased and a t quite high concentrations (33 per cent or more) most monoolefins show press u r e drop a n d g u m formation in less than 4 hours (experiments 4, 5, 7, 11, 19, 23, 32, etc., and Figure 1). Straight-chain olefins having the double bond at the end of the chain are more s t a b l e than those having the double bond elsewhere (compare experiment 19 with 23,28, and 32). For e q u a l concentrations by volume and for olefins of s i m i l a r structure, those of low molecular weight seem to s h o w l e s s stability than t h o s e of higher molecular weight (compare experiment 4 with 22). For equal molecular concentration, however, it would appear that the stability may be about the same (experiments 3 and 22, 6 and 23). The comparison of 2 - p e n t e n e and trimethylethylene (experiments 2, 10, etc.) would seem to indicate t h a t branched-chain hydrocarbons are less stable than the corresponding straightchain. On the o t h e r hand, diisobutylene is as stable as 2-octene though less stable than 1-octene. NAPHTHENIC MONOOLEFINS. The data on cyclohexene (experiments 33 to 35) indicate that a double bond O I 4 in a cyclic ring is perTIM( HOUR; haps s o m e w h a t less FIGURE2. DIOLEFINS stable than in an aliDhatic olefin, but the hifference is 'not marked. Compounds containing a double bond in the side chain (experiments 36 and 37) seem to behave like the simple olefins. AROMATIC MONOOLEFINS.Attaching a benzene ring to an oleiin seems to decrease the stability markedly, though the effect of structure introduces differences among the individuals. All compounds tested of this class seem less stable than the simple olefins, and a double bond adjacent to the ring involves high instability, particularly in styrene but also marked in I-phenyl-1-propylene (experiments 38 to 44). ALIPHATIC DIOLEFINS. Diolefins as a class are markedly less stable than monoolefins, but the position of the double
November, 1933
INDUSTRIAL AND ENGINEERING CHEMISTRY
1237
s'~"
(experiments 61, 87 to 89). A s i m i l a r observation has been made by Zelinskii and Titova (26). Apparently polymerization mithout oxidation may occur $ with l-phenyl-1,3-butadiene, as e with i s o p r e n e a n d s t y r e n e (steam-oven evaporation), although the experimental technic does not preclude the presence of small amounts of oxygen. -TETRAHYDRONAPHTHALENE. CYCLIC DIOLEFINS.Three FIGURE 3. IN RhTE OF PRESSURE DROP This substance seems hardly to d i o l.e f i n. s of this .class . mere WITH LENGTHOF INDUCTION PERIOD fit in any of the above classes. It s t u d i e d , all containing conis of interest as illustrating (in jugated double b o n d s . 1,3Cyclohexadiene seems somewhat less stable than the com- high concentrations) high gum formation with relatively little parable aliphatic diolefins (compare experiments 61 and 62 oxygen pressure drop, and high gum formation after aging. MIXTURES OF HYDROCARBONS. The data on mixtures of with 46, 47, and 49). l13-Cyclopentadiene and l,&phenylbutadiene show the largest amounts of gum (for equivalent hydrocarbons are not sufficiently complete to permit generaliconcentrations) of any hydrocarbon studied. It is interesting zations, but the experiments carried out are interesting; that the oxidation of 1,3-cyclohexadiene apparently comes to a since cracked gasolines are undoubtedly complicated mixtures, standstill when a certain amount of oxygen has been absorbed it is desirable to scrutinize the data carefully.
bonds is important in determini n g stability. C o n j u g a t e d double bonds (compare experiment 45 with 46, and 49 with 50) introduce e x t r e m e instability, while a compound containing double bonds widely separated is almost as stable as an average monoolefin. (Compare also di-
TABLE11. DIOLEFINS
.
7-
No.
-OOXYQEN BOMB-EVAPN. Time InGum HYDROCARBON IN cf duePresby Boiling In STEAMheat- tion sure steam range mixture OVEN ing period drop oven %by Moles/ Ma./' L b p . in: Mo;;,lOO C. ool. liter 100 C E . Hours Hours (kg. 89 cm ) 4 0.5 20 (1.4) 296 48.3-49.7 10 1.03 4
Name
45
2,3-Pentadiene
46 47
1,3-Pentadiene 1,3-Pentadiene
40.7-41.9
48
2-Methyl-1,3-butadiene (isoprene)
......
49
2,CHexadiene
50 51 62 53
1,5-Hexadiene (diallyl) 69.0-59.3 l,5-Hexadiene (diallyl) l,5-Hexadiene (diallyl) 2,3-Dimethyl-1,3-butadiene 69.8-70.8 2,3-Dimethyl-1,3-buta.diene 2,3-Dimethyl-l,3-buta.. diene
54 55
77-79
86-89b
.
1998 2201
1.00
132
4
0.25
65 (4.6)
2444
10
0.88
2
4
0.1
70 (4.9)
1113
0
64
75
10 33 67
0.84 2.80 5.61
1
..
4 4 4
4 4 2
5 (0.35) 6 (0.35) 20 (1.4)
6 50 303
0 .. ..
7 9 24
4 19
2
0.18
.
4
0.75
20 (1.4)
133
.. ..
..
5
0.44
4
0.25
65 (4.6)
479
.. . .
..
10
0.89
0.0
65 (4.6)
1039
.. ..
..
.. .. .. .. .. ..
.. .. .. 747 ..
40
10
. . .
2
0.09
10
0.46
17 10 40
0.78 1.22 4.88
10 40
1.05 4.20
2
. . ..
4 6.75
654 4085f 9122f
4 4
0.0
0.25
35 (2.5) 100 (7.0)
1491 5542
..
......
..
0.25
50 (3.5)
3845
63
Dipentene
175-179
10
0.62
2
64
l-Phenyl-1,3-butadiene 81-82d
10
0.71
357
4
65
Tetrahydronaphthalene Tetrahydronaphthalene
10
0.73
0
4
40
2.91
.
4
d
A t 9 mm. pressure.
>4
1.0
40 (2.8)
12
1 . 2 5 65 (4.6) 0.25 60 (4.2) 0.0 70 (4.9)
80.2-80.8
On evaporation in porcelain dish.
5 (0.35)
4 4 4
1,3-Cyclohexadiene 1,3-Cyclohexadiene
b A t 13 mm. pressure. c 642 mg. per 100 00. a t 28 months.
5.0 2.5
61 62
.
,
4
40.1-41.6
a
..
70 (4.9) 70 (4.9)
287
0
..
TEST (MONTHS):12 16 20 24
Milligramr/l 00 cubic centimeterse 19 24 68 67
0.25 0.25
0
2,6-octadiene 1,3-Cyclopentadiene 1,3-Cyclopentadiene
205.7-206.2
2
8
5 5
1.10 4.00
11
59 60
66
-STORAQE Initial 4
62 224 423 1950
618 3409 4366
.. .. ..
NOTESO N PREPARATION
..
From trichloro2 pentanol [butyrchloral ($0) Me-
.. ..
D kX'yh'r a t i o n
-
+
MVCI 1
with iodine au c a t a l y a t (11, 19).
159 321
....
324
..
116
127 268 390 39 . . .. .. .. .. .. . . .. .. .. . .
.. .. ., .. . . .
..
.. . .
..
..
.. . .
,
22
.. .. .. .. . .
..
.. ..
..
..
.. ,. .. ..
D e h y d r a t ion with iodine as c a t a l y s t (19, 21, 81)
(4)
Obtained from A . L. Henne
,
.
O b t a i n e d from A. L. Henne
,.
.. ..
By depolymerization of dicyclopentadiene obtained from Genera Motors Corp. 8 19+ 289 518f 560 681 664 Dieth l a n i l i n e ., umd' for re2974 moval of HBr (6) 3 47 64 81 342 3 5 0 C R e f r a o t i o n a tion of Eastman Kodak uroduct 343 1070 1819 2378 4048 5672 MkgCl subs t i t u t e d for MeMgBr ( 1 3 ) . formation of ad intermediate halogen compound was observed ,.
..
..
.. ..
..
..
..
10 (0.7)
0
0
15 (1.1)
560
..
6
0
1085 1498
0
26 113+
332 R e f r a c t i o n a tion of Eaatman Kodak product
.. .. .. ..
JNDUSTRIAL AND ENGINEERING
1238
TABLE 111. MIXTURES OF OLEFINS BOVB--
-OXYQEN
Time of
No.
cCON0TITIJXNT HYDROCARBONSIn mixture heatIng Name
Induoperiod tion
% b y Moles/ uot. .^
67
Trimethylethylene 1-Heptene 1-Octene 2-Octene 4-Octene Diisobutylene Gasoline 68 Trimethylethylene 1-Octene Diisobutvlene 69 Trimethilethylene Diisobutylene 70 2,3-Dimethyl-1,3butadiene Diisobutylene Gasoline 71 2,3-Dimethyl-1,3butadiene Diisobutylene Gasoline 72 2,3-Dimethyl-1,3butadiene 1-Heptene Gasoline 73 2.3-Dimethvl-1.3' butadiene ' Trimethylethylene 2-Pentene 2-Hexene Diisobutylene Gasoline ~
1z
.liter .-\
$Pres!A;
Hours
by
(kdq. M*./ Lb
Hozlr8
Gum
$"o",",:
in. cm.) looCc.
l.ld
12 0.84 12 0.75
14,5
7,0
35 ( 2 , 5 )
380
0'5
70 ( 4 ' 9 )
255
60 ( 4 , 2 j
116
10 0.64 12 0.78 33
..
33
2.17
67 2 20 78
0.18 1.30\
2
0.18
31
..
..
4
1.25
30 ( 2 . 1 )
4
oo
60 (4.2)
239
O.0
35 (2.5)
221
0.25
60 (4.2)
249
2 0.18 31 , . I 7 \ 67
..
2 12
0.18 1.13
4 50
..
In experiment 67 in which the total olefin content is 67 Per cent, with no individual hydrocarbon Present in more than 12 per cent, the induction period is much longer (7 hours) than was found to be the case for any individual olefin' tested in 67 per cent concentration (compare experiment 7 ) . Since it is unlikely that any individual olefin would be present in a gasoline in amount greater than 12 per cent, the experiment indicates that a cracked gasoline containing simple olefins only would probably be quite stable, even if the total olefin content was very high. I n experiments 68 and 69 one olefin whose induction period is fairly short in the concentration employed (trimethylethylene) has its induction period decreased if the remaining hydrocarbons are unsaturated rather than saturated (compare with experiment 11). Experiments 70 to 72 containing a small amount of a diolefin together with varying amounts of olefins indicate again that the induction period of the diolefin is shortened by the presence of the olefins (compare these experiments nith 53) * INHIBITORS. It is not the purpose of this paper t o present
CHEMISTRY
Vol. 25, No. 11
a complete discussion of gum inhibitors or to compare their relative effectiveness, but a few experiments are given to indicate the mechanism by which they act. The inhibitor employed in this work was a-naphthol. Comparison of the data in Table IV indicates that the entire action of inhibitors is to increase the induction period without, however, changing the rate of pressure drop aftkr the induction period or affecting the gum formation once the induction period is over. Experiments 78 to 83,84 to 86, and 87 to 89 are particularly interesting. In the first series the heating was discontinued when the pressure had dropped to a definite value. The results show the effect of varying concentrations of inhibitor in lengthening the induction period without, however, affecting the rate of pressure drop or of gum formation a t the end of the induction period. The other series show similar results (Figures 2 and 4). These data seem of importance in connection with the commercial uses of inhibitors and will be discussed further below. AGINGTESTS.Unfortunately, aging tests could be carried out on only a limited number of samples because of lack of sufficient amounts of most of the hydrocarbons. The following general conclusions may, however, be noted : (1) No aliphatic monoolefin in 10 per cent concentration forms appreciable gum in a year of storage although tetramethylethylene begins t o form gum fairly rapidly after a year. (2) Cyclohexene in high concentrations and most of the olefins containing a benzene ring form appreciable gum in a few
~ ~of the ~ diolefins l l form gum in storage in any concentration although 1,b-hexadiene is much the more stable in this respect. (4) Inhibitors strongly retard gum formation. m
CORRELATION OF AGINGAND OXIDATION TESTS At the beginning of these experiments it was hoped that some reasonable correlation might exist between the oxidation test and the actual gum formed on aging. While this work was under way, however, investigations by Bridgeman and others (2) were presented which indicate that no quantitative relationship should be expected to exist between any simple oxidation test and gum formation in storage. For example, it has been shown that the time necessary for the contents of the oxidation bomb to come to temperature equilibrium is in some cases an hour or more and, consequently, all of the short induction periods correspond to some unknown temperature lower than that of the bath, Furthermore,.it has been shown that the effect of temperature on the induction period for different hydrocarbons is not the same and, therefore, it would not be expected that a quantitative
TABLE IV. OLEFINSCONTAINING INHIBITOR OXYO YO EN BOXBEYAPN. Time InGum IN of ducPresby HYDROCARBON--NAPH-STEAM heattion sure steam Name Inmixture THOL OYBN ing period drop oven Lb./sq. in. Mg./ % b y Moles/ Mg./ Mg./ vol. liter liter 1OOcc. Hours Hours (kg./sq. cm.) 100 cc. a-
No. 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 0
b
7 -
10 (isoprene) 10 2-Methyl-l,3-butadi ene 10 2 4-Hexadiene 10 2:CHexadiene 10 2 4-Hexadiene IO 2'4-Hexadiene 10 2'4-Hexadiene 10 2'4-Hexadiene 10 2'4-Hexadiene 10 2:4-Hexadiene 10 1 3-Cyclopentadiene 10 1'3-Cyclopentad1ene 10 1:3-Cyclopentadiene 10 1 3-Cyclohexadiene 10 1'3-Cyclohexadiene 10 1:3-Cyclohexadiene 10 Phenylethylene (styrene)b 10 Phenylethylene (styrene) b On avaporatioqin porcelain dish. Probably contain~ngethylben~ene.
1.00 1.00 0.88 0.88 0.88 0.88 0.88 0.88 0.88 0.88 1.22 1.22 1.22 1.05 1.05 1.05 0.86 0.86
0 100 0 100 0 20 40 60 80 100 0 20 100 0 20 100 0 100
132 2 5
3 1 1 11 6
4 0.25 4 >4 4 0.25 4 >4 1.75 0.25 6 4.5 8.25 6.75 10.75 9.25 11 9.5 12.6 11.5 4 0.25 5 1.75 9.5 9.5 4 0.25 4 0.5 4 3 4 1.5 4 4
65 (4.617 5 0 35) 70 [4:9)
......
40 (2.8) 45 (3.2) 40 (2.8) 45 (3.2) 40 (2.8) 45 (3.2) 60 (4.2) 60 (4.2) 0 (0) 35 '2' 5) 35 1215) 35 (2.5) 20 (1 4 10 (0171
2444 162 1113 3 595 663 495 623 652 644 408544487 9 1372 f 1822 f 16554955 5
.Initial
STORAG T ~ S (MONTHS): T 8
4
12
16
20
24
36
Milligrams pet cubic centimetera 159 0 0 0
... ...
...
... .... .. ..
.. . t
9 1 2 0 0
321 174 64 0 108 0
... 3 ... 0 ...
723 f 1781 2342 190 185 168 127 116 75 23 9 3 207 7 3 7
... . . . ... 10
...
... ... ...
... ...
242 14 14 17 6
,..
530 16
IO
13 1
572 17 17 20 10
390
...
... ... ... ...
... ... . . . ... ... ... ...
...
... ... ... . . .
268 80
583 26 18 29 8
6
... .. 603 123 20 112
16
... ... I..
624
... ... ...
...
hovernher, 1933
I N D U S T 11 1 A L A N D E N G I N E E R I N G C 11 I3 M I S T R Y
1239
* , . a
i $,=a
$
g ,e
$
F I G U R E 4. PRESSUlrE CURVES FOR 2,4-EEXhDIENE Relation between ienath of induction period and amount oi inhibitor i s shown.
relation would exist between oxidation tests made at a single temperature and storage tests carried out a t a lower ternperature. Nevertheless, the results obtained in this investi(ration bring out several interesting points:
should be added in sufficientquantity to stabilize the gasoline for periods well above the exuected normal time of storage. - if eventual gum formation is to Ije avoided. ( 5 ) It would not appear that a simple relation exiats between leneth of induction Deriod and time of stabilitv in Ftorwe. G6olincs may. mme;)ver. be exvected to show Larked diffzr-
(1) All mixtures which have formed considerable pym in
torminnti0nbfthe;nduction period a i d the rate of gum formatintion
( 2 ) Some blends which have shown;el&vely lod kum formation after several months of aging followed by a relatively high rate of gum formation, have also shown a short induction period followed by a rapid pressure drop. Others have shown a steady and fairly slow increase in gum during wing and B slow rate of pressure -drop by the oxidation tea< (Compare oxpedinents 44 and 46 with 34,40,and 63.) (3 No blend showing an induction period of 4 hours or more has ormed appreciable gum in storage.
siter the induction period is over.
1
COXLUSIONS It is somewhat doubtful to what extent the d a b on pure hydrocarbons can be applied to commercial gasolines, since these can never be assumed to contain only one individual olefinic compound. Certain probable conclusions may, liowever, be suggested: (1)
The substances chiefly responsible for (rum formation in
(2). Except perhapsin special ca%s, pum formation is always associated with oxidation. (In two experiments in which 2 , 4 hexadiene and 1,3-c clopentadiene in 10 cent concentration were tested by the tomb test hut by su stitutmg nitrogen for oxygen. no droD in wessure was remrded a t the end of 4 and 9.6
g..,
(3) Stahihtion of an unstable gasoline may be effected by
befoie an unstable asolinc begins to break down. Since commercial gasoline is 8equently stored for considerable length of time (a yenr or more), it would nppcar easentist that inhibitors
Racmvso June 20. 1933. Presented i o part before the Division of Petroleum Chemistry at the 80th Meetiog of the Amerioan Cbemical Society. Cincinnati, Obio, September 8 t o 12, 1930.
CRACKING UNIT
