January, 1935
INDUSTRIAL AND ENGINEERING
of any metals capable of withstanding the temperature encountered.
ACKNOWLEDQMENT The boiler plant here described has been designed, built, and operated by the staff of the Dow Chemical Company.
CHEMISTRY
15
The author is indebted to many individuals of that organization for the foregoing information, but particularly to Richards, Holser, and Griswold of the Engineering Staff and to Grebe and his associates of the Research Department. R ~ C ~ I VNovember ED 15,1934.
Inhibitors in Cracked Gasoline 111. Storage Stability as Related to Induction Period and Critical Oxidation Pot entiall C. G. DRYER,J. C. MORRELL, GUSTAVEGLOFF,AND C. D. LOWRY,JR. Universal Oil Products Company, Riverside, Ill.
T
HE e s t i m a t i o n of the
A test was made in which samples of five representative gmolines were stored in bottles vented to fhe air for 20 months. Some of the samples contained inhibitors. Among samples of any one gasoline, a relationship is found between induction period, as determined in steet bombs at fo0"C. and 100 pounds oxygen pressure, and storage life. An induction ~ period , of 300 minutes or a n increase in initial induction of 200 minutes obtained by addition of a n inhibitor produced a storage life of over a year in small containers in all but one of the gasolines studied. An untreated gasoline high in copper-dish gum had short storage life despite a 245-minute induction period. The stability of the samples in storage are found to be related, with some exceptions, to the critical oxidation potentials of the inhibitors present when the inhibiting substances are added in equimolecular concentration.
stability of a c r a c k e d gasoline in storage from a test which may be carried out within a short t h e is a major problem in petroleum refining. The tests most generally used a t the present time accelerated Oxidation Of the usually in a metal bomb according to the procedure of H ~ Fischer, andBlackwood @),orin glass by the method of Voorhees and (I6)* Dataon the relationship of the latter procedure to s t o r a g e c o n d i t i o n s have been published by Rogers, Bussies, and Ward (1.4). They conclude that, in storing small gasoline samples~ "the life is a linear function of the i n d u c t i o n period.)) O n t h e other hand. Winning and Thomas (IY), using essentially the method of Hunn, Fischer, and Blackwood, found that the storage life of many of their samples would h e up "not a t all with the breakdon" (induction period). The use of accelerated oxidation tests and prediction of stability from induction period has received considerable criticism. It has been contended that the severe conditions used, 100' C. and usually 100 pounds per square inch (7 kg. per sq. cm.) oxygen pressure, are too far removed from conditions of storage to make predictions of value (1, 10, 19,
1
For Parts I and I1 of this seriea, see literature citations 6 and 9.
PROCEDURE Five typical cracked gasolines were e m p l o y e d . They were produced on commercialunits, shipped to the laboratory mediately after production, and kept under nitrogen until be emphasized used. It that fresh gasolines are essential in investigations of storage s t a b i l i t y , a n d failure to observe this precaution has seriously reduced the value of some P ' $ ~ ! a ~ ~ o f ~ ; e used s in the present study were of the following types: 1. Pennsylvania untreated 2. Pennsylvania va or-phase,
treated with fuller's earti 3. Midcontinent untreated s u P ; f ; r i ~ ~ ~ ~ t treated i n e n twith 3 pounds kg*)Of g3 per cent (la4
5. West Texas reformed, untreated
The gravities and distillation ranges of these gasolines are presented in Table I. TABLEI. PROPERT~ES OF GASOLINES Wl8T
16).
Further work was desirable, therefore, to determine the significance of accelerated testing by the method of H u m , Fischer, and Blackwood, which has been in use in this laboratory for more than three years. This paper reports the r e sults of storage tests carried out to obtain information regarding the relationship between induction period, rate of gum formation, and storage stability of cracked gasolines. I n an earlier investigation (9) a correlation was established between the ability of inhibitors to raise the induction period of a cracked gasoline and their critical oxidation potentials. In the present work a relationship was sought between the
~ o t e n t b l o fan inhibitor and its ability to s t a b i l i z e g a s o l i n e in storage.
MIDCONTINSNT
za:[iy 0 A. p I A. 8.T.'M. loo-&
distn.. O C. (" F.) Initial b. p. % distilled over: 10
50 90 End point
PBNNBYLVANIA Tsxas
Refined Unrefined 0.7511 0.7715 56.9 51.9
Refined Unrefined Reformed 0.7470 0.7208 0.7358 57.9 64.8 60.8
41 (106) 37 (99)
43 (109) 36 (97)
30 (86)
I
65 149) 94(201) 129 264) 150 302) ::1 {!2"6] 201 394 192 378) 195(383) 217 4231 209 1408) 230 (446)
only the Midcontinent untreated had been sweetas the products ened. The gasolines had the same used in the studies on (Iw). Storage was in gallon (3.8-liter) bottles of brown glass which
16
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 27, No. 1
TABLE11. INHIBITORS IN PENNSYLVANIA UNTREATED GASOLINE 1,5-DIInhibitor: Concentration, %: Original properties: Induction eriod min Gum, mg.y!OO ci.: ’ Copper-dish Air-jet Color, Saybolt Octane No. Peroxide No. After 2 months: Gum mg./100 cc.: Copper-dish Air-jet Color, Saybolt Octane No. Peroxide No. .4fter 5 months: Gum, mg./100 cc.: Copper-dish Air-Jet Color, Saybolt Octane No. Peroxide No. After 9 months: Gum, mg./100 cc.: Copper-diah Aik-jet Color Saybolt Octade NO. Peroxide No. After 11 months: Gum mg./100 cc.: Copper-dish Air-jet Color, Saybolt Octane No. Peroxide No. After 16 months: Gum, mg./100 cc.: Copper-dish Air-jet Color, Saybolt Peroxide No. After 17 months: Gum mg./100 cc.: Cdpper-dish Air-jet Color, Saybolt Peroxide No.
NONE
..
a-
QALLOL QUINONE
HYDROXYNAPHTHALENE
0.0016 0.00138
0.0020
0.00138
0.0018
PYRO-
HYDRO-
CATE-
NAPH-
CHOL
THOL
%HYDROXY1.3-nr.~ METHYLBENZENE
0.00154
2-AMINO&NITRO-
P-CREBOLPHENOL PHENOL 0.0013 0.0012 0.0019
WOOD-TAR ANILINE DISTILLATE 0.0012 0.0050 0.0100
60
265
80
195
130
170
95
80
80
130
90
150
173 1 21 71
4 1
3
117 21 71 0
1 21 71 0
146 1 21 71 0
4 2 19 71
30
20 71 0
55 1 21 71 0
67
21 71 0
17 1 21 71 0
57
0
2 1 21 71 0
324 7 23 69 4.70
7 0 25 71 0.14
164 0 25 71 0.36
52 1 23 71 0.17
129 1 24 71 0.78
90 21 70 0.30
332 2 21 70 2.70
324 10 22 70 6.20
616 810 10 56 49.5
27 72 0. I9
i
87 2 25 69 2.50
7 0 22 70 0.27
292 462 15 63 35.0
498 608 15 63 35.6
618 276 13
.. .. ..
..
.. ..
..
..
.. ..
.. ..
21 3 26 68 0.21 17 7 26 67 0.26
.. ..
7 2 27 0.39
.. ... . ..
153 42 23 5.0
928 160 21 1:iz
.. .. ..
..
0
.. .. .. .,
.. 1 .
1
..
586 416 16
.. .. ..
5815
..
.. .. .. I
.
..
..
..
..
.. ..
..
..
0:59
..
..
..
8
20
107 16 18 67 3.10
..
..
41
.. .. .. ..
..
.... ..
1
..
..
..
..
were not filled above the point of widest diameter and were vented by inserting glass capillaries of 0.25-mm. bore through the corks, allowing access of air but restricting loss by evaporation. The storage room was warmed in cold weather to about 24°C. so that the temperature varied only between this temperature and the highest reached in summer-about 35’. Gravities and A. S. T. M. distillations a t the end of 17 months indicated a loss of about 10 per cent of the gasoline by evaporation during the test. Some influences were excluded in this study (iron or its oxides or sulfides, water, caustic soda, or plumbite) which might be present and accelerate deterioration in commercial storage. I n other respects the test. was more severe than storage under practical conditions, as the gasoline was warmed during the cold months and was more exposed to oxygen than is gasoline in large tanks. Rogers, Bussies, and Ward found much slower change during storage in a 6000-barrel tank than in smaller containers. It is probably not practicable from analytical tests to predict the exact life of gasoline in large-scale storage. What was sought in this study was a means of predicting that stored gasoline would not deteriorate harmfully before the expiration of a definite period of time. During the test, determination of the peroxide content of the gasolines was made every 2 weeks. As the peroxide content of cracked gasoline has been found to be a good index to the progress of its deterioration, peroxide number was used as a guide in making other tests-gum, color, octane number, aldehyde, and acid. Complete anlysis was made every month in samples in which the peroxide content was rapidly increasing, and less frequently when a low peroxide number indicated that little change was occurring. Data on air-jet gums were obtained by A. S. T. M. method
..
..
49:5
.. I .
375 10 23 70 5.30
320 6 10 71 0.74
238 2 21 70 4.40
138 0 25 71 0.27
55 1 25 71 0.24
577 314 10 61 43.5
45 12 9 69 2.0
664 766 16 59 51.5
26 0 26 71 0.19
26 71 0.21
117 56 11 66 10.30
.. ..
164 28 22 66 7.10
0.29
.. ..
.. .. .. ....
..
..
.. ..
473 320 16 58 36.5
30 10 26 67 0.39
..
..
.. ..
.. ..
.. .. ..
..
.. ..
.. ..
....
.. ..
.. ..
.. ..
71 0
..
..
... .
.... ., ..
2
0
0
.. .. ..
..
0 21
21 71 0
.. .. .. .. .. .. ..
0
230
..
.... .. ..
.. ..
..
.. ..
.. ..
..
..
..
I .
.. ..
.. .. I
.
..
..
21 71
0
7
0
18 3 26
68
112 20 22 6.80 ,.
.. .. ..
A (2), which gives values about 50 per cent higher (3) than the newly adopted standard, formerly method B. Peroxides were determined, as in earlier work, by the method of Yule and Wilson (18) and octane numbers by the research method, as the motor method was not in use a t the time these tests were started. The tests for aldehyde and acid were made for their value in indicating the mechanism of gum formation and have already been published (4).
PENNSYLVANIA UNTREATED GASOLINE To the untreated Pennsylvania gasoline were added, in equimolecular proportion, eleven inhibiting substances covering a wide range of critical oxidation potentials. Tests were also made with a wood-tar distillate inhibitor (8). Selected data from the storage of these samples are presented in Table 11; it will be found that the copper-dish gum figures are in some cases lower after 4 months than after 2. This is an apparent, rather than a real reduction, since a t that time the Atlantic Refining Company modification of this test was adopted (7). This method often gives lower, though more reproducible, values than older procedures. The data in Table I1 show that during storage of all samples of this gasoline there was a period of slow change corresponding to the induction period in accelerated aging (oxygen bomb). During this time, which may be termed the “storage induction period,” the peroxide number increased slowly and but little air-jet gum formed. However, even in this period there was definite formation of peroxides and production of a weighable amount of gum. At the end of this period, usually marked by a peroxide number of about 3, the rate of peroxide formation accelerated, air-jet gum developed more rapidly, copper-dish gum increased, color de-
Mmon LAUOKATOHY OF UNIVERSAL 011. I’F~XXJCTS COMPANY WXEREOCTANE Vai.u.u~sOF GASOLINEY ARE DETERMINED
preciakd, and antiknock value dropped. The existence of two stages in the deterioration of gasoline is shown by the behavior of the sample inhibited with pyrogallol, which had a peroxide number of only 0 39 after 16 months and was stili in its “storage induction period,” During the following month, honwer, thp rapid deterioration began, with a sharp rise in peroxide number and gum. This sudden change in the rate of depreciation of gasoline is also shown in the graphs of data from this study already published (4). TABLE 1x1. CORRELATION
OF CRITICAL OXIDATSON POTENTIAL AND EFFECTSVENEBS IN STORAGE
(Pennaylvanis untreited sasohnel
2.5
Pyroaallol 1.5.Dihydroxynsphfhalens a-Naphthol 2-Hydrory-l,3-dimethylhennene
a%%* 2-Aiiiino-4-nitropheool Anillne
0.600
ZB5
0.673 0.797
195
170
0.895
95
1.088
SO
1.03s
1.107 1.135
Woad-tar distillate: 0.010% ... 0.005% ... * sample inadvertently spoiled b 0 months. 8 mg. 13 months. 5 mg.
so
130
so
230 150
17
.
~
B
4
4
4
17
17
17
17
(9 mO.,0 . 3 7 ~ (Q m.,4 n,gl 8 10 9 0
S
z
a
3
1
4
2 5
2 8
2 5b
I
2
3
s
3 8 8 3
15
15
..
110
16
9
9
I I
7
2
8
P
9
2
s
By t:he time air-jet gum had accumulated in this gasoline to the extent of 10 mg. per 100 ec., its period of slow change was about a t an end, and, when 15 mg. had formed, rapid deterioration had begun. In a few cases an apparent decrease in gum was found after 10 mg. had formed, possibly because of $light variations in the manner of carrying out the test. No such decrease occurred in any case after 15 mg. of grim
had developed. Rogers, Ilussies, and Ward (14) give 10 mg. as a “reasonable upper limit” of gum tolerauce in gasoline, although Marley and Gruse ( i f ) and others (%I have indicated that more may sometimes be allowed wit.hout harm, depending on Ihe condition of the motor. Winning and Thoinas (17) used as a criterion the time their gasoline sdmpies were stored before forming 10 and 20 mg. of air-jet gum. I n Table I11 the data on the storage of the Pennsylvania untreated gasoline (considering all data and not only those presented in Table 11) are summarized by rates of peroxide formation and storage life (to formation of 10 and of 15 mg. of gum by method A). The samples are listed in such a way as to allow their comparison on the basis of the critical oxidation potentials of the inhibiting substances. In an earlier publication (9) it was pointed out that a parallelism betwecn inhibiting effectiveness and potential could be observcd between closely related compounds hut was not always found among substances of widely different structure. The same conclusion may be drawn from the results of storage tests, although not enough compounds were studied in storage to check all the earlier work. Comparing hydroquinone and catechol, gasoline inhibited with the former had the longer storage life, as would be predicted from its lower potential hut not from its shorter induction period. The other substances studied, as shown in Table 111 were decreasingly effective as the potential increased, with the exception of 2-amino-4-nitrophenol, which, both in accelerated testing and in storage, was more effective than its potential would lead one to expect. As stated in the former paper (Q), this may be due to a tendency to ioniaation induced by the nit.ro group. The group of inhibitors having potentials below 0.8 volt were particularly effective in stored gasoline; they had previously been found to be effective in increasing induction period. Considering all results, the critical oxidation potential appears to bo a useful means of systematizing information on inhibitors but not an absolute index of antioxidant activity. The induction periods of these gasoline samples are shown
IN DU STR IA L A N D E N GIN E ER IN G CH E MI STR Y
18
in relation to their storage life in Table IV. It should be remembered that, except for the wood-tar distillate, the inhibiting substances were used, not in equal, but in equimolecular concentrations. There is a definite relationship between induction period and time before the development of 10 mg. of air-jet gum in storage; the only exception is the sample inhibited with hydroquinone, which, as earlier work showed, could not be rated by the bomb test, probably because it is directly affected by the high concentration of oxygen used there (6,9).
The storage data on these gasolines are summarized in Table VI with reference to the time required to reach specific peroxide concentrations and to accumulate 10 and 15 mg. gum by air jet. The storage stabilities of the samples of Pennsylvania treated gasoline were about equal to those found with samples of the untreated gasoline of the same origin having similar induction periods. Thus an induction period of 285 minutes denoted a storage life of 15 months as measured by the time elapsing before the formation of 10 mg. of air-jet gum. The untreated Midcontinent gasolines behaved differently. Despite an induction period of 245 minutes, it had deteriorated in 5 months, forming both peroxidic compounds and gum. The inhibited samples were more stable. The gasoline had an initial copper-dish gum of 92 mg., which rapidly increased, and which may be an indication of instability in storage and may be. of value in such a case as this where the induction period is not a sufficient criterion. The treated Midcontinent gasoline, produced by the same cracking installation and from the same stock as the untreated product, was of shorter induction period, probably because it had been sweetened. It was much more stable than the untreated gasoline, lasting 12 months alone and longer when inhibited. The West Texas reformed gasoline was unstable by itself but responded well to inhibitors. The inhibited samples, in line with their high induction periods, formed peroxides slowly. About 10 mg. of air-jet gum formed in 9 months, however, although the gum content did not further increase in 6 additional months, and the gasoline protected by inhibitors was usable for more than 15 months.
TABLEIV. INDUCTION PERIODAND STORAGE LIFE TIM^ TO REACH INDUCTION AIR-JETGUMOF: PERIOD 10 mg. 15 mg. Min. --Months-
INHIBITOR Pyrogallol Wood-tar distillate, 0.01% 1,5-Dihydroxynaphthalene or-Na hthol w o o c h a r distillate, 0.005% 2-Amino-4-nitro~henol Catechol 2-Hydroxy-l,3-dimethylbenzene Hydroquinone None a 13 months 6 mg. b Sample inAdvertently spoiled.
265 230 195 170 150 130 130
Over 9 b 9 9 5
80 60
6
17
17 16
110
95
..9 9
4
8 4
3
3 6
3
3
STORAGE OF OTHERGASOLINES To samples of the treated Pennsylvania gasoline, the Midcontinent gasolines, and the reformed West Texas product, catechol and wood-tar distillate,inhibitor were added in proportions giving equal induction periods. The initial properties of the gasolines and the changes occurring during storage are shown in Table V. TABLE V. Gasoline: Inhibitor: Inhibitor concn., %:
-PENNSYLV.4NIA
TREATEDWood-tar None Catechol distillate . 0.00092 0.0047
.
Original properties: Induction eriod, min. 185 290 Gum, mg.7100 eo.: Copper-dish 8 1 Air-jet 0 0 Color, Saybolt 30 30 Octane No. 74 74 Peroxide No. 0.04 0.04 After 2 months: Gum mg./100 cc.: Copper-dish 29 13 Air-jet 4 0 Color, Saybolt 30 30 Octane No. 71 Peroxide No. 2.09 0:54 After 4 months: Gum, mg./!OO cc.: Copper-dish 72 8 Air-jet 3 0 Color Saybolt 30 30 Octade NO. 71 72 2.58 0.50 Peroxide No. After 7 months: Gum, mg./lOO cc.: 2 Copper-dish 30 2 Air-jet 14 Color, Saybolt 25 30 Octane No. 68 71 Peroxide No. 0.88 0.66 After 9 months: Gum, mg./100 cc.: 162 9 Copper-dish 2 168 Air-jet 28 17 Color, Saybolt 62 Octane No. 71 Peroxide No. 36.5 1.27 -4fter 11 months: Gum mg./100 cc.: Copper-dish .. Air-jet .. Color, Saybolt .. .. Octane No. Peroxide No. 6i:o 1:iis .After 15 months: Gum, mg./!00 cc.: Copper-dish 1093 20 Air-jet 640 10 Color. Saybolt 5 25 Octane No. Peroxide No. i72 3 .'20 5 This figure, given as 5.50 in citation 6, was
.. ..
STORAGE OF GASOLINES
-hfIDCONTINENT
None
..
Vol. 27, No. 1
UNTREATED-
Wood-tar Catechol distillate 0.005 0,025
TREATEDWood-tar Catechol distillate 0,005 0.025
-fi$IDCONTINE.\IT
None
..
-WEST
None
..
TEXASREFORMEDWood- t ar Catechol distillate 0.005 0.025
285
245
400
340
205
350
345
40
290
310
6
92
5
3
21
65
10
18 63
68 0
10
30 74 0.04
46 1
0
0.11
2 20 63 0.11
0.11
214
211
1
5
281
30 72
17 62 5.50
17
493 8 17 60 8.90
0 0.25
0
30 72 0.20
3 2 30 72 0.32 6 7 29 71 0.75
....
6
171 18 17
8
11 25 2 .'60 in error.
19
62 2.08
63 4
o:is 263 2 17 63 1.49 87
10
2 21
68 0.13
68 0.13
68 0.13
15 0
35
0 20
80 0 19
0:54
0135
57
112
65 1.39
21 67 0.40
20
55 4
28 3 18
21 66 1.01 234 1 21
..
58
61 5.95
285
62 4 17 60 7.70
58 12 15 60 7.88
42
81
17 59 11.4
16 59 11.40
22 62 3.75
144 72 17
286 130 16
72 12 19
22.0
16 96 53 57.0
..
1:47
408 1
0 20
....
..
.. .. .. .. ..
28:7
14 ._
23:O
0 21
21
15 63 5.10
..
..
0 19 62 0.18
0
19 63
0
64 2.30
0.66
1 20
34
23 7
65
2.80
66
6:60
74 0.00
210 52 I5 70 3.52"
0.29
347 138 -15 68 6.00
20 3 15 67 0.49
312 268 Yellow 64 10.9
0
66
24
0
.. ..
67 0.54
0.43
.. .. ...
..
..
.. ..
0:?3
0148
14 7 20
20
0:85
0:iO
19
..
66
..
16 6
15
6
19
....
.. .. .. .. ..
0 13 74 0.00
11 0 16 0:21 11 5
0
12
74 0.00 12 6 15 73 0.18 17 6
16 73 0.22
73 0.20
6 6 16
16
16
8
2
71 0.14
71 0.10
7
8 13 17
lo 15
o:ii
o:i3
.. .. ..
..
o:ii 14
.. .. o:is
lo 15
10 7 17
0:ig
0:io
January, 1935
I N D U S T R I A L *4 IS D E N G I N E E R I TABLEVI.
GASOLINB:
19
RELATION OF INDUCTION PERIOD TO STORAGE STABILITY
CONCN.
INDUCTION COPPER-DISH
%
Min.
GUM M ~ . / 1 0 0cc.
Pennsylvania clay-treated: Wood-tar distillate inhibitor
0.0047
285
6
Catechol No inhibitor Midcontinent untreated: Wood-tar distillate inhibitor Catechol No inhibitor Midcontinent treated:. Wood-tar distillate inhibitcr Catechpl No inhibitor West Texas reformed, untreated: Wood-tar distillate inhibitor
0.00092
.....
290 185
1 8
0.025 0.0050
PERIOD
340 400 245
3 5 92
0.025 0.0050
345 350 205
55 21 46
0.025
310
10
0,0050
290
10
No inhibitor ..... After 17 months, peroxide number 0.21. b After 17 months, peroxide number 0.40.
40
68
..... .....
Catechol
, ISTK1 '' Iv G C H E M
TIMEr o REACHPEROXIDE No. 1 -Months
OF:
TIME TO REACHAIRJ E T GUMOF: 10 mg. 15 mg. Montha-
-
2
5
10
14
21
15
9 1
13 2
17 8
15 7
(19 mo., 10 mg.) 16 9
5 4 1
7 6 2
7 12 5
12 13 5
20 20 6
13
16 16 12
18 18
4 3.5
