INDUSTRIAL A N D E N G I N E E R I N G C H E M I S T R Y
914
Vol. 41, No. 5
gasoline. Sludge oxidation products tend to settle out and adhere to container surfaces on standing. This mag in part a t least for the good initial stability of uninhibited plant ~ ~ ~ E ~ ~~'50lbCf&ocfk~e~";Pe'~~n~1~~~~~~~~i~~~~~~;Og004b~~: & ! i ~ ~ ~ , samples. However, these points require clarification based on Conditions: Varied. 100-gal. tanks (1-inch water layer) 90% full initially. furt,her study. half emptied of gasoline after 1 week, 90% emptied after 2 weeks, and refilled I n review, the problem of st,abilizing tetraethyllead is closely with fresh gasoline to original volume ac end of third week; cycle repeated for total test period of 24 weeks] akin t o the problem of stabilizing leaded aviation gasoline. Inhibitors of the type described show definite stabilizirig action in Not Drum Further 1 Inhibiteda Drum fol:2 TEL Properties Inhibited Stabilization both media. There mould appear to be definite hericfit to be Final tank drainings gained from inhibit,ing tetraethyllead, not only t o prevent it's Gasoline ex oil-watcr interface Wt., g. 2100 2800 possible sludging and degrading effect on aviation gasoline stability, Appearance but t o prevent its partial conversion into less effective antiknock La,'~~$$"i;~~$''hl~f~;~~e~~~~?~ dark color materials such as trialkyllead salts. Water drainings, g. 4400 3000 Sludge. g. 150oa 500a From a practical standpoint also, inhibited tet,raethyllead would be much less likely t o contribute t o lead precipitation in aviation Analysis Filteredof drainings dry solids, Torn of above gasoline storage. Result,s presented in Table XI1 indicate that Cloudy gasoline 0.13 0.05 Water drainings 0.14 0.07 tank scale deposits, normally rich in lead compounds arid requiring 22 (330 g . ) Sludge 55 (280 9.) special precautions in disposal, are materially reduced in lead conLead content in solids, c/ow Total Pb tent by use of an effective inhibitor for tetraethyllead in the Cloudy gasoline 5.6 3.3 Water drainings 8.1 0.6 finished gasoline. Additional advantages might be gained b y Sludge 1. 0 0.4 earlier incorporation of the inhibitor directly irit,o tli(> wtmTrialkyl P b in sludge 0.0014 0.0010 Trialkyllead content, %w ethyllead. Gasoline filtrate 0.0007 0 0004
Table XII.
Effect of Inhibitors in Minimizing Lead Deposition in Tank Storage
Water filtrate 0,0013 0.0012 Total lead content of water filtrate, % w 0,000.5 0.0006 a On each filling with gasoline, 2,4-dimethyl-6-terf-butJ.1Dhenol was added in equivalence to l % v of T E L content.
or not the inhibitor was used up in stabilizing tetraethyllead during storage. The results of these tests are given in Table XI. For these aviation blends, the oxidation products in tetraethyllead appear active a t some intermediate state, but not initially or on prolonged aging. The inhibited samples showed little depreciation during storage, indicating that the inhibitor was not destroyed in stabilizing tetraethyllead. This interim adverse effect of the uninhibited lead samule. although noted previously, has not yet been entirely explained. It is seemingly related to the nature of the intermediate oxidation products (possibly bismuth impurities initially present in tetrsethyllead) and the degree of their dispersion or suspension in
Literature Cited (1) Coordinating Research Council, "Report on 1944 I k w r t Storage Tests on Aviation Gasolines."
(2) Ethyl Corp., private communication. (3) Lowry, C. D., Jr.. Egloff, G., Morrell, J. C., and I>rser, C . G., ISD. ENG,C H E M . , 804-8 ~ ~ , (1933). (4) Maycock. R. L., private communication. ( 5 ) Morrell, J . C., Dryer, C. G., Lowry, C. D., Jr., rind 1':gloff. G . , I N D . E K G . C I I E M . , 26, 497-503 (1934). ( 6 ) Velde, H. Von, Oel u. Kohle, 40, 10-15 (1944). (7) \Valtera, E. L., U. S.Pat,ent 2,361,337 (Oct. 24, 1944). (8) Walters, E. L., Minor, H. B., and Yabroff, D. L., "CIicniist,ry of Gum Formation in Cracked Gasoline." IND. ENO. C m M . (t,o be published). (9) Walters, E. L., Yabroff, D. L., and Minor, H. R., I / i f / / . ,40, 423-x (1948). (10) Yahroff, D. L., and Walters, E. L., Zbid , 32, 88 8 ( l 9 i O ) . (11) yule,J -4 L , and l\rilson, C . p , J ~ .l b, i t i . , 23, 12.54 o ( I ( I . < I ) . R~~~~~~~september 20, 1948.
Inhibitor oncentration ability R. H. Rosenwald and J. R. Hoatson UNIVERSAL OIL PRODUCTS COMPANY, RIVERSIDE, ILL.
T h e relation between the extent of stabilization as measured by the accelerated oxygen bomb and inhibitor concentration s log can b e expressed b y two general equations, l o g y = r x andy = a 6% c log x , where the two variables arey, the length of the induction period, and x, the inhibitor concentration. The applicability of these two equations was demonstrated for thermally cracked and catalytically cracked gasoIines with four antioxidants.
+ +
THE
+
accelerated oxygen bomb test is a n important means of estimating the stability of a cracked motor fuel as shown by the time of storage a t atmospheric conditions before the gum content becomes excessive. The length of the induction period as determined by this test, along with certain other information, +
is indicative of the degree of sbabilitv. The stability oi i t motor fuel can be increased by the addition of antioxidants; the irirwise in a normal gasoline is dependent on the effectiveness tind (soricentration of the antioxidant added. This paper considers the relation between the concentration of inhibitor and the extent of stabilization as measured by the length of the induction period. It has been generally considered that the length of the induction period is nearly proportional to the amount of inhibitor added. The work done with catechol in an untreated Pennsvlvania fuel (2) and with 1-naphthol in blends of straight-iun and cracked fuels (1) indicates such a relationship. A re-euaminu tion of the relationship, however, has led to the belief that a better correlation can be obtained. It has been observed that deviation from the linear relationship does occur, and that the CUI'VP obtained upon plotting induction period against concrntr:i t i o n IP
May 1949
INDUSTRIAL AND ENGINEERING CHEMISTRY
not a true straight line but a curve whose slope diminishes with increasing values of concentration. The observation means that the first increment of inhibitor added produces a larger increase in length of induction period than do succeeding increments. In view of this fact, i t is of interest t o obtain a n expression t h a t affords a more descriptive picture of this phenomenon. This has been accomplished by the formulation of two equations:
140
120
z
0 80 c V
+ s log 2 y = a + bs + c l o g s log y = r
n
z
915
4c
(1) (2)
2c
I80
140
120
100
VI
F3 80
$d $60
w
2 0 40
F
0
az
20
Figure 1.
Figure 2.
Stabilization of Thermally Cracked Motor Fuel
Stabilization of Thermally Cracked Motor Fuel
where the two variables are y, the length of the induction period expressed in minutes, and 2, the inhibitor concentration expressed in parts of inhibitor per million parts of gasoline. These two equations are not interchangeable and each has merits of its own. Equation 1 was developed in a purely empirical manner. Because the curve defined by this equation is a straight line on log-log paper, this form lends itself readily t o practical use in correlating concentration and stability. However, the equation is occasionally unreliable at low inhibitor concentration, and is not applicable as zero concentration is approached. Equation 2 can be developed in a semimathematical manner by consideration of the kinetics of the reactions taking place. According t o Equation 2, a linear proportionality is approached a t high inhibitor concentrations. The question arises whether the induction period increase or the induction period should be used in the calculations, particularly in case of Equation 1. I n this work, the motor fuel was treated to remove natural inhibitors and the induction period was 105 minutes or less. It is believed that in the range of about 50 to
Figure 3.
Stabilization of Thermally Cracked Motor Fuel
CHEMISTRY
Vol. 41, No, 5
mally cracked and with a catalyt,ically cracked fuel. The stabilization as afforded by varying concentrations of four inhibitors, N,S'di-sec-butyl-p-phenylenediamine, N-n-butyl-paminophenol, tert-butylcatechol, and 2.4-dimethyl-6-tert-butylphenol, is shown graphically on both coordinate and logarithmic scale in a series of figures (Figures 1 to 6). The curves drawn on the coordinat,e scale figures represent that defined by Equation 2 and the constants in Table I. Both equations give a reasonably accurate relatioriship as shown by the root mean square deviation. I n comparing potencies in any given gasoline, large positive values of the constants are indicative of a potent, antioxidant. 1 1 0 ~ ever, every constant in either Equation 1 or 2 is not at maximum or minimum values for any one inhibitor. I n Equation I , high values of r are associated with low value? of s, and in Equation 2, high values of a are accompanied by low values of c. In comparing inhibitor potencies, one is interested in the siabilization as brought about by a loninhibitor concentration and one term may command more attention, as is the case of the r term in Equation 1. The values of the constants are a function not only of the antioxidant but also of the properties of the gasoline. I n fact, the inhibitor response of a fuel can bo characFigure 4. Stabilization 'of Catalytically Cracked Motor Fuel terized by evaluating the effect of an inhibitor as measured by the equation. The following example is offered t o demonstrate that such characterization, 100 minutes, the induetion period is of no great signiparticularly by Equation I, can be made. I t is generally realized ficance, for induction periods of this length were obtained that maximum benefit of a n antioxidant is obtained by addition regardless of the extent of oxidation of the gasoline tested. before any peroxidation of the gasoline has taken place. This For this reason the induction period as such was used in fact is shown by storage a t atmospheric temperature of a n uninpreference to the induction period increase. hibited freshly treated gasoline for periods of 0, 2, 6, and 11 days The applicability of Equations 1 and 2 has been demonstrased prior t o addition of N,N'-di-sec-butyl-p-phenylenediamine. As in a number of gasolines. The data summarized in Table I shown in Figure 7, maximum stabilization was obtained by imnicare representative of results that can be expected with a ther-
INHIBITOR CONCENTRATION,RPM
Figure 5.
Stabilization of Catalytically Cracked Motor Fuel
Figure 6 .
Stabilization of Catalytically Cracked Motor Fuel
INDUSTRIAL AND ENGINEERING CHEMISTRY
May 1949
917
Table 1. Evaluation of Constants Constants, Equation 1 Motor Fuel
Inhibitor
Thermally cracked
Catalytically cracked
T
N,N'-di-sao-butyl-p- henylenediamine N,n-but yl-p-arninop {enol tert-Butylcatechol 2 4-Dimethyl-6-tert-butylphenol dennofuroxan N,N'-di-sec-butyl-p-phenylenediamine N,n-butyl-p-aminophenol tert-Butyloatechol 2,4-Dimethyl-6-tert-butylphenol
1 ,858 1.815 0.938 1.495 1.468 1.615 1.190 0.971 1.054
diate inhibition, with decreasing stabilization as the storage period prior to inhibitor addition was lengthened. The values of the constants for the four sets are as follows: Time of Storage, Days 0 2 6
11
7
1.657 1.624 1.415 1.019
8
a
0.519 0.512 0.563 0.653
-204 -268 -218 - 77
'
b
0.970 0.719 0.782 0.790
C
307.8 334.7 250:3 105 4
It is generally observed t h a t the value of s is slightly increased and the value of r is decreased as the gasoline deteriorates, It was considered of interest to test the applicability of these equations with an antioxidant which possesses an entirely different structure from t h a t of the easily oxidizable phenol and amine derivatives considered so far. Such a compound is benzofuroxan, which is a n oxidizing reagent but still possesses an appre-
a
8
- 147
0,474 0.528 0.826 0.570 0.446 0.482 0.713 0.761 0.67
-402 -197 - 33 - 75 -176 - 194 - 50 68
-
Root Mean Square Deviations, Min. Equation 1 Equation 2
Constants. Equation 2 b c
1 382 1.155 2.083 1.593 0.335 0.709 1.696 1,742 1.082
326.4 541.5 211.7 140.4 133.2 245.3 228.1 84.8 101.6
34.1 57.6 44.6 27.9 18.8 12.4 23.5 39.8 25.4
22.3 27.3 39.0 9.2 8.9 13.5 26.7 36.5 17.4
ciable potency as antioxidant. As shown in Figure 8, the stabilization as obtained with benxofuroxan in a thermally cracked fuel follows the same pattern and can be expressed by both Equations 1 and 2. This fact indicates that the logarithmic or exponential relationship is not due to same phenomenon involving the extraction of a loosely bound hydrogen atom of the antioxidant under conditions of the accelerated test. It has been shown that the stabilization of a cracked motor fuel with varying inhibitor concentration can be evaluated by use of several equations which involve some exponential function of the concentration. The following observations indicate t h a t this relationship does apply in the case of pure hydrocarbons. The extent of the stabilization of Tetralin a t 100' is directly dependent on the inhibitor concentration (5). I n the case of Tetralin i t was calculated t h a t the linear relationship is predicted regardless of the particular oxidation mechanism involved. The stabilization of styrene with respect to oxidation is controlled by a linear function of the inhibitor concentration (4).I n the case of cyclohexane in the accelerated oxygen bomb ( I ) , Equation 1 can be applied t o give an excellent correlation of the data. T h e use of diisobutylene has led to results that can be expressed by the logarithmic function. As shown in Figures 9 and 10, the length of the induction period can be expressed by either a linear or logarithmic dependency in the case of tert-butylcatechol and 2,4-dimethyl-6-tertbutylphenol, whereas the results with N,N'-di-sec-butyl-p-phenylenediamine can be accurately expressed only by the logarithmic function. The values for the constants in Equation 1 are as follows: tert-Butylcateohol 2,4-Dimethyl-6-tert-butylphenol N,N'-di-8ec-butyl-p-phenylenediamine
r
9
2.021 1.423 2.033
1.044 1.012 0.752
When the s value approximates 1, the following condition is present: Figure 7. Stability of Motor Fuel Stored Prior to Addition of N,N'-D!'-sec-butyI-p-phenyIenediamme
I
logy = r + s l o g z y = 1WZ" y = r'x
I
I
I
INDUSTRIAL AND ENGINEERING CHEMISTRY
918
Figure 9.
Vol. 41, No. 5
Stability of Diisobutylene
Owing to an intercept oi about zero on the coordinate scale (Figure 9), the relationship with tert-butylcatechol and 2,4-dimethyl-6-tert-butylphenol appears t o be linear, whereas with N,N’-di-sec-butyl-p-phenylenediamine, which possesses an s value of 0.752, the linear relationship fails. It is believed that the formulas presented will be found of value in determining an adequate yet economical dosage of antioxidant in commercial batches of gasoline.
Literature Cited
i 70
50
20
l N r i BiTOR
10
5
CONCCNTRATION,
2
PP
M
Figure 10. Stability of Diisobutylene
(1) Dryer, C. C . , Lowry, C . D.. Jr., Egloff, G., a n d Morrell, J. C . , I X D . E N G . C H E M . , 27, 315 (1935). R. H., “Stabilization of Styrene,” payer yresent’ed (2) Egloff, G . , ~ ~ ~ J . ~c.,~L 1 1~ c., D., ~ j r , ,~and D~ ~ c, ~ c,, ~ , ~ (4)~RoSe11Wald , before Division of Organic Chemistry, 109th Meeting of ~1~ Ibid., 24, 1375 (1932). CHEM.SOC.,Atlantic C i t y , N. J., April 1946. (3) George, P., and Robertson. A . . Proc. Roy. SOC.(London), 185, 309 (1946). R r c r r v r ~ iSeutemher 24, 1948.
Relation of tivators Roger W. Watson and Theodore B. Tom STANDARD OIL COMPANY (INDIANA), WHITING, IND.
C
ERTAIN metals, particularly copper, exert a powerful pro-oxidant effect on many organic compounds. I n the presence of oxygen and copper such compounds deteriorate in quality and in many cases form undesirable color and residues. In this way the presence of copper may lead to marked deterioration of a petroleum product, particularly cracked gasoline, notwithstanding the presence of ordinarily adequate amounts of inhibitor. The use of copper chloride sweetening has been shown t o impart small quantities of capper to gasoline stocks. The amount necessary to catalyze oxidation is considerably less than one part per million; hence careful attention must be directed to removing any metal ions thus introduced. An early approach t o the problem of removing dissolved copper salts from copper-sweetened oils involved treatment with aqueous solutions of sodium, zinc, or ferrous sulfides, or of sodium carbonate. From time to time other agents for washing out copper ions have been disclosed, among which are solutions of thiols ( 8 ) , aminothiols ( 7 ) , and sodium and potassium arsenites (20). The addition of a compound having a tendency t o combine with the metal to form a stable nonionic complex is another and singularly successful approach to the problem of combating metal catalysis. Such additives, called metal deactivators, were first described in 1939 by Downing, Clarkson, and Pedersen (9).
Their work and that of others so succesafully illuminated the harmful role of certain metals in the storage and handling of gasoline that the incorporation of metal deactivators in some fuels has become commonplace. Catalytic deterioration of motor fuels-especially those containing cracked components-is often exhibited when such fuel: are brought into contact with transportation and storage containers and fuel-system parts such as feed lines, strainers, pumps and carburetors fabricated from copper or its alloys. Oxidation and gum formation are particularly severe where the copper parts are new or where a single fill of gasoline is permitted to remain in contact with the metal for several weeks. Instances of trouble have been reported with new vehicles on display, with fueled military vehicles after a n extended period of water or rail transport, and with marine craft in which the fuel systems remained filled but inactive over the winter months. The Ordnance Department has recognized this problem and specifies (19) that fuel purchased for storage in new fuel system6 either be straight-run (virgin) or contain a n oxidation inhibilor and a metal deactivator. One of the chief uses of metal deactivators is the protection of these so-called drive-awa? gasolines. Metal catalysis is also responsible for increased rates of deterioration in lubricating oils where copper and lead appear either
