FIGURE1.
COMPARISON OF
CYCLOHEXENE ANTI SECONDARY GASOLINESTANDARDS
A Pure
:rcL O H F X E N ~0 . .00~ ~1cwaoozs
GAMLINE
0.001 0.01
0.001
000s
Hydrocarbon Standard for Evaluating Inhibitors
0.003
a015
,
0.000 0.09
a 0.
C. G . DRYER,C. D. LOWRY, JR., GUSTAVEGLOFF, A m J. c. MORRELL Universal Oil Products Company,
R
ESEARCH on gasoline antioxidants has been handiRiverside, Ill. capped by lack of a standard method of comparison. In this paper a reproducible means of rating such substances is proposed, based on the use of a pure hydrocarbon. was reproducible and uniform a t all times. In this paper a Inhibitors have been evaluated by the induction period means of preparing such a standard is presented. Inhibitors which they produce when added to cracked gasoline. When are tested in a blended gasoline whose susceptibility to inhibia gasoline of short induction period and high inhibitor sus- tors is fixed by relating it to that of a pure hydrocarbon, ceptibility is available and tests are performed before the cyclohexene. As cyclohexene is unvarying, the gasoline gasoline changes substantially in properties, as in an earlier standard can be reproduced a t any time. investigation in this laboratory (I), the method is fairly satisfactory. Storage under nitrogen will extend the useful CYCLOHEXENE AS PRIMARY STANDARD life of the gasoline, but this precaution does not permit its use as a standard for a long period. It is therefore difficult, Cyclohexene was selected as a base material for inhibitor if not impossible, to obtain identical results a t different times. evaluation after testing a number of hydrocarbons. Since The difficulties encountered in using gasoline as a base we are concerned with inhibitors for cracked easoline. which material are clearly shown in the work of Rogers and Voor- are high in olefins, the standard should preferably be’an unhees (3) in which inhibitors were compared in different con- saturated hydrocarbon. 2-Octene can be purchased but is c e n t r a t i o n s i n a n u m b e r of expensive and cannot readily be c r a c k e d gasolines. As they brought to the desired purity. Reproducible gasoline blends have been prestate, “unfortunately many of 2-Pentene and trimethylethylene . pared whose inhibitor susceptibilities as measthe data were obtained over an are too low-boiling for convenured by a-naphthol bear a definite relationship extended period of time, using ience. Other available comto that of cyclohexene. different stocks, so that a direct pounds, such as styrene, indene, comparison of the compounds or cyclopentadiene, are so reacAs a measure of inhibiting value, the “cyclois n o t always possible.” tive that troublesome p r e c a u hexene number” is proposed. This is the number Scheumann (4) e n c o u n t e r e d tions are necessary to keep them of minutes which the induction period of cyclothe same difficulties, and his free from peroxides and polyhexene would be increased by the addition of comparisons of gum reduction mers; these precautions must 0.002 per cent of an inhibitor as calculated from by various inhibitors are lessbe observed if accurate results ened in value by the fact that are to be obtained. tests made in reference gasolines whose relationhe used many gasolines. Cyclohexene is not expensive, ship lo ryclohexene has been determined by standThe objection to testing inand by a single fractionation the ardization with a-naphthol. h i b i t o r s in gasoline would be c o m m e r c i a l p r o d u c t can be Cyclohexene numbers are given f o r forty-one eliminated if it were possible to brought to a boiling range of less representative inhibitors. use a standard gasoline which than 0.1’. It has an induction 315
I N D U S T R I A L A N D E N G I N E E R I N G C H E ,If I S T R Y
316
period of 45 minutes, varying * 5 minutes, and when free from peroxides gives reproducible induction periods with inhibitors. After use in inhibitor testing, it may be recovered by steam distillation followed by fractionation through an efficient column, leaving a residue of not less than 10 per cent. When recovered in this way, the product is peroxide-free and constantboiling. As explosive products, probably of peroxidic nature, are formed by oxidation in the bombs, the steam distillation is an important precaution. SECONDARY GASOLINE STANDARDS By adding fresh unstable cracked gasoline to straightrun gasoline, it was found possible to prepare blends whose inhibitor susceptibility bore a definite relationship t o that of cyclohexene. Four blends were made by adding two Pennsylvania, one West Texas, and one Midcontinent cracked gasoline to a Pennsylvania straight-run gasoline. The properties of the gasolines are shown in Table I.
Data comparing the response of these standards to inhibitors with the behavior of cyclohexene both with anaphthol and with other inhibitors are presented in Table 11. TABLE 11. EFFECT OF IXHIBITORS
Phenyl-n-naphthylamine 4-Hydroxyl-l,3-dimethylbensene Isoeugenol Eugenol ---RESPONSE
OF
15 3 65 70
11 3 63 90
7 3
71 55
SECONDARY GASOLINE STlNDARDS
Concn.
135 65 50 15
TO INHIBITORS-
MidWest contiTexas Pennsylvania nent Stand- Standard Standard I I1 ard
% MID-
StraightCracked RENENT run 1 11 FORMED CRACKED 63.4 63.8 62.8 59.8 59.3 0.7260 0.7245 0.7238 0.7397 0.7416 28 13 21 Yellow -2
%lt:'(Savbolt) Gum,mg. 100 cc.: Copper dish 0 Air jet 0 Octane, No. (motor method) 46 Induction period, min. N o break
0,002 0.002 0.002 0.002
.
I l I T l A L INDCCTION PERIOD, MINUTES
PENNSYLVANIA TEXAS CONTI-
Gravity, OA. P. I.
-
RESPONSEOF CYCLOHEXEKE TO IXHIBITORS Induction PeConcn. riod Increase % Mifl Cyclohexene alone, initial induction period, 45 min. Cyclohexene and or-naphthol 0.0005 170 0.001 315 0.002 595 0.004 1070 0.005 1295
TABLE I. PROPERTIES OF GASOLINES WEST
Vol. 27, No. 3
16 6 69 180
....
Gasoline alone
80
130
175
380
INDUCTION PERIOD INCREASE. MINUTES
Gasoline and a-naphthol
0,0025 180 195 160 175 355 0.005 360 310 320 0.010 600 610 585 640 0.015 830 830 830 790 0.020 1035 1040 1020 1060 0.025 1210 1280 1290 1200
0.01 Phenyl-o-naphthylamine 4-Hydroxyl-1,3-dimethylbenzene 0.01 0.01 Isoeugenol Eugenol 0.01
160 180 75 40
185 185 50 50
175 165 75 60
105 I00
._. 20
A. 8. T. M. 1 W C C . DISTILLATION
Initial B. P. % dktilled over: 10 50 90 E n d point
'C. 52
78 121 167 199
97
'C. 46
58 136 172 57 135 250 121 250 121 250 333 180 356 173 343 390 193 379 194 381
62 109 174 200
O F .
126
'C. 37
OF. 99
'C. 36
O F .
O F .
115
'C.'F. 34 93
144 57 228 121 345 190 392 203
135 250 374 397
The blends contained the following proportions of the cracked gasolines in the straight-run gasoline: 30 per cent Pennsylvania I; 33 per cent Pennsylvania 11; 34 per cent West Texas; 72 per cent Midcontinent. The first three blends gave satisfactory results, the fourth did not. The first three were standardized by comparing their response to a-naphthol with that of cyclohexene. Over a wide range of concentration it was found that one part of a-naphthol in cyclohexene produced almost exactly the same increase in induction period as did five parts in the gasoline standards. This relationship is shown graphically in Figure 1. a-Naphthol is an inhibitor of intermediate effectiveness and is more suitable for use as a correlating inhibitor than a more powerful or a weaker one. Comparison of inhibitors was made entirely on the basis of the increase produced in the induction period. The fact that the initial induction periods of cyclohexene and of the three blends were not exactly the same did not interfere with this comparison. The differences in inhibitor susceptibilities between cyclohexene and the secondary standards are not greater than the differences between individual cracked gasolines. The susceptibility of the gasoline standards is midway between the lowest and the highest that were found in testing a number of gasolines. The blend prepared with Midcontinent gasoline was apparently too stable and did not give the same values with anaphthol as did the other blends, nor did it respond to the same degree to other inhibitors. This gasoline was not suitable, therefore, as a secondary standard. It appears that only unstable cracked gasolines should be employed as materials for the preparation of secondary standards.
Each value in Figure 1 and the tables is the average of a t least four determinations. As shown in Figure 1, with anaphthol there is good agreement between the increase in induction period in cyclohexene and in the West Texas and Pennsylvania secondary gasoline standards over the entire range of concentrations studied. With the other and much weaker inhibiting substances, there is considerable discrepancy between cyclohexene and the gasolines although these three secondary standards agree among themselves quite closely. It is the increase in induction period, produced by an inhibitor in a secondary reference gasoline which has been standardized against cyclohexene using anaphthol, rather than the increase produced when the inhibitor is tested in cyclohexene itself, that is taken as the measure of inhibiting value. CYCLOHEXENE NUMBER -4s a reproducible measure of the effectiveness of gasoline inhibitors, the "cyclohexene number" is proposed. This is defined as the calculated increase in the induction period of cyclohexene which 0.002 per cent by weight of an inhibitor vould produce; the calculation is based upon the induction period experimentally determined in a secondary reference gasoline which has been related to cyclohexene by the use of a-naphthol. This concentration of inhibitor in cyclohexene (0.002 per cent) is selected because it is sufficient to show definitely the effect of weak inhibitors and yet does not give inconveniently long induction periods when powerful antioxidants are used. The cyclohexene numbers of compounds which have been tested for inhibiting value run up to 1500 minutes. The data in this paper were obtained using the equipment described earlier (1) in which gasoline contained in a glass bottle within a steel bomb is exposed t o oxygen a t 100" C. and 100 pounds per square inch (7 kg. per sq. cm.) pressure. To determine cyclohexene numbers, a cracked gasoline of low induction period should be tested in the bomb with
March, 1935
INDUSTRIAL AND ENGINEERING CHEMISTRY
0.01 per cent a-naphthol. If the increase produced in the induction period is less than the increase given by 0.002 per cent a-naphthol in cyclohexene, the gasoline should be blended with a straight-run product in such proportion that the increase in the gasoline becomes the same as that in cyclohexene when a-naphthol is used in the proportions stated. Comparison should then be made of the induction period increases in cyclohexene and in the blend with a t least one higher and one lower concentration of a-naphthol, using five times as much in the gasoline as in cyclohexene. If the values obtained in cyclohexene and in the gasoline are in agreement, the gasoline blend may be used as a reference standard for evaluating other inhibitors. The described procedure gives a secondary standard in which the induction period increase, using 0.01 per cent a-naphthol, is equal to the induction period increase obtained in cyclohexene using 0.002 per cent a-naphthol. This proportionality must hold not'only a t one concentration of inhibitor but over a wide range of concentrations. This ratio of one to five is not obligatory, but gasoline secondary standards may be prepared in which the effectiveness of a-naphthol in the gasoline bears some other ratio to its effectiveness in cyclohexene. If the one to five ratio is used, any inhibitor whose cyclohexene number is to be determined is added to the gasoline standard in 0.01 per cent by weight. Secondary standards should be kept under nitrogen to prevent deterioration. If, during storage, the inhibitor susceptibility of a secondary standard changes slightly, it may be adjusted by adding a small amount of either the cracked or the straight-run component and restandardizing against cyclohexene with a-naphthol. Many inhibitors are sparingly soluble in cracked gasoline, and it is desirable, particularly in experimental work, first to dissolve them in a solvent before addition t o the gasoline to be inhibited. In an earlier publication (1) attention was drawn to the fact that certain solvents sometimes reduced the power of inhibitors t o increase induction period. This phenomenon has been further investigated in order to find solvents without this action. Table I11 shows the effect of solvents upon the action of a wood tar inhibitor ( 2 ) in gasoline. The solvents alone had no effect upon the induction period. I n each case 0.025 per cent of the inhibitor, dissolved in 5 cc. of the solvent in question, was added to 200 cc. of an acid-treated cracked gasoline and the induction period determined.
TABLEIV. COMPARISON OF SOLVENTS FOR INHIBITORS INHIBITOR (0.01%) 2-rimino-4-hydroxytoluene
1,5-Dihydroxynaphthalene Pyrogallol Thiodiphenylamine 4-Chloro-2-aminophenol 2-Amino-4-nitrophenol m-Aminophenol
Chloroform Acetone Methyl ethyl ketone Toluene
Earlier work had shown that benzene has no harmful effect, and Table I11 indicates that chloroform and toluene are also satisfactory. The superiority of methyl ethyl ketone over acetone suggested the use of a higher ketone, and hexone (methyl isobutyl ketone) was found to dissolve many inhibitors not soluble in benzene and to give little or no change in induction period. Hexone and benzene were therefore adopted for use. Comparison of induction periods given by a number of inhibitors using these two substances as solvents and testing in a Pennsylvania secondary gasoline standard (I) are shown in Table IV.
,$fin. 1380 1345 1060 1045 1075 1095 770 765 400 405 350 310 320 330
Benzene Hexone Benzene Hexone Benzene Hexone Benzene Hexone Benzene Hexone Benzene Hexone Benzene Hexone
INDUC-CYCLOTlON
HEXENE
130
..
Hexone Hexone Hexone Hexone Hexone Hexone Hexone Hexone Benzene Hexene
1530 1150 1065 1066 1045 975 950 875 740 730
1400 1020 935 935 915 845 820 745 610 600
Hexene Benzene Hexone Hexone Benzene Hexone Benzene Hexone Benzene Hexone
725 665 605 545 455 440 410 330 315 315
595 535 475 415 325 310 280 200 185 185
Phenyl-a-naphthylami Benzene 2-Hydroxyl-l,3-dimeth~benzene Benzene 2-Amino-4-nitrophenol Hexone - Pyrogallol dimethyl ether Benzene Heptylresorcinol Benzene Hexylresorcinol Benzene 2-Hydroxy-1,4-dimethylbenzene Benzene - Thymol Benzene m-Toluylenediamine Hex o ne 4-Hydroxy-1,2-dimethylbenaene Benzene
315 305 305 280 270 270 260 255 250 240
185 175 175 150 140 140 130 125 120 110
235 230 215 195 195 185 185 180 180 165 165
105 100 s5 65 65 55 55 50 50 35 35
....
No inhibitor Inhibitors. 0.01%:
Pyrogallol 1 5-Dihydroxynaphthalene datechol a-Naphthol 2,4-Diaminodiphenylamine p,p'-Diaminodiphenylamine Thiodiphenylamine p-Phenylenediamine o-Aminophenol w-Aminodiethvlaniline
m-Phenylenediamine Butylguaiacol Gallic acid Orcinol Resorcinol monoethyl ether Resorcinol Resorcinol monomethyl ether Isoeugenol Eugenol 5-Hydroxy-1 ,a-dimethylbenzene 8-Naph th ol
105 440 140 260 225 325 410 425 340 390 440
INDUCTION PERIOD
SOLVENT PERIOD"N0.b Min.
INDUCTION PERIOD
+
SOLVENT
The differences when the two solvents are used are seen to be slight. As a general rule, benzene was used with inhibitors which it would dissolve, and hexone in other cases. In Table V are given the cyclohexene numbers for representative inhibitors calculated from tests made in secondary gasoline standards. TABLE V. CYCLOHEXENE NUMBERS
TABLE111. EFFECTOF SOLVENT ON INDUCTION PERIOD Gasoline alone Gasoline inhibitor, no solvent
317
a
b
Hexone Benzene Hexone Hexone Benzene Hexone Benzene Benzene Benzene Benzene Benzene
With Pennsylvania secondary standard I. Induction period increased, in minutes.
It is recognized that further work is desirable on this method of preparing secondary standards and rating inhibitors to confirm the conclusions reported here, LITERATURE CITED (1) Egloff, G., M o r r e l l , J. C., Lowry, C. D., Jr., and Dryer, C. G., IND.ENG.CHEM..24, 1375 (1932). (2) Lowry, C. D., Jr., and Dryer, C. G., U. S. P a t , e n t s 1,889,835and 1,889,836( D e c . , 1932). (3) R o g e r s , T. H.,a n d V o o r h e e s , V., IXD. Eim. CHEM.,25, 520 (1933). (4) Scheumann, W. W., Oil Gas J.,31, No.46,22 (1933). RECEIVEDOctober 13, 1934. Presented before the Division of Petroleum Chemistry a t t h e Twelfth Midwest Regional Meeting of the American Chemical Society, Kansas City, Mo., May 3 t o 5, 1934.
