Based on the favorable results in rate studies, a preliminary cost estimate was performed to determine whether or not further development of a lignite process was warranted. The hypothetical process used for economic evaluation involved the rraction of sulfur with dried lignite at 750’ C.: assuming b>-product yields that represented a lOy0loss in sulfur and no credit for potential recovery. Results indicated that the process on this basis wcsuld be competitive with current market prices at a plant capacity above 20,000,000 pounds per year. ‘I‘he favorable indications provided by the rate studies and rhe cost estimate are not by themselves sufficient to establish the suitability of lignite as a raw material or thecomplete feasibility of a lignite-based process. Information is lacking on the yields of carbon disulfide from sulfur that can be achieved using various lignite chars, a factor which is highly important to the economics of the process. In addition it is necessary to demonstrate the technical feasibility of continuously admitting ’
sulfur and char to a compact reaction system to capitalize on the high rates that have been demonstrated. The solutions to these problems are major objectives in a pilot plant program which has recently been initiated. literature Cited (1) Chem. Eng. News 41, 25-6 (1963). (2) Haines, H. W., Jr., Znd. Eng. Chem. 5 5 , 44-6 (1950). (3) Kirk, R. E., Othmer, D. F., eds., “Encyclopedia of Chemical Technology,” Vol. 3, pp. 142-8, Interscience Encyclopedia,
New York, 1949. (4) Madon, H. N., Strickland-Constable, R. F., Ind. Eng. Chem. 50, 1189 (1958). (5) Munderloh, H., Brennstoff-Chem. 38, 372-3 (1957). (6) Needham, L. W., Hall, N.W., Fuel 14, 222-30 (1935). (7) Strickland, J. R., ed., “Chemical Economics Handbook,” Vol. 6, p. 625, Stanford Research Institute, Menlo Park, Calif., 1962. RECEIVED for review March 19, 1964 ACCEPTEDAugust 6, 1964 52nd Meeting, A.I.Ch.E., Memphis, Tenn., February 1964.
EFFECT OF ORGANOSULFUR COMPOUNDS ON THE RATE OF THERMAL DECOMPOSITION OF SELECTIED SATURATED HYDROCARBONS B. M . FABUSS, D. A.
DUNCAN, AND J . 0. S M I T H
Monsanto Research Gorp., Everett, Mass.
C. N . S A T T E R F I E L D Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Mass.
%
The effect of addition of 0.001 to 10 weight of an organosulfur compound upon the thermal decomposition rate of each of several saturated pure hydrocarbons was studied b y batch experiments a t 800” F. and elevated pressure. The effects of benzenethiol or teff-butyl disulfide upon n-hexadecane, 5-n-propylnonane, and decahydronaphthalene were studied in detail. Decomposition rates of the branched-chain paraffins were accelerated; those of the saturated hydrocarbons were inhibited. The sulfur compounds less stable than the hydrocarbons all acted in the same direction.
fuels used in high speed flight vehicles may become heated to several hundred degrees Fahrenheit before combustion by aerodynamic heating of the fuel tank, by absorption of heat to cool lubricating oil or portions of the engine, or by all three. As a result, gums, sediments, or deposits may be formed in the fuel and cause excessive pressure drop through nozzles and strainers or even complete plugging. T h e reactions and conditions leading to the formation of these undesirable products are but poorly understood. T h e effects stem in part fro:m precursors formed by air oxidation on storage, a reaction which may be catalyzed by trace metal contaminants or by container materials. Some air oxidation may also occur in flight vehicle tanks during aerodynamic heating. T h e susceptibility to gum and deposit formation also varies with the kinds of hydrocarbons present in the fuel and is increased by the presence of various contaminants containing sulfur or nitrogen. The fact that deposit formation is also a function of previous time-temperature history of the fuel and of various interactions among oxygen, contaminants, catalysts, and inhibitors leads to highly complex phenomena YDROCARBON
Some proposed mechanisms are discussed.
and sometimes seeming contradictions between the results of different investigators. Most studies have been made with actual fuels, with or without various deliberately added model contaminants. T o help clarify the situation, it is desirable to know the rate of decomposition of selected pure hydrocarbons in the absence of oxygen and how these rates are affected by the presence of specific sulfur compounds which typify the kinds of compounds that may be found in hydrocarbon fuels. Beyond this, hydrocarbons are used in a variety of technical applications which require a fluid thermally stable a t high temperatures, and it is important to know the effects of contaminants on decomposition rate. Sulfur compounds are a universal contaminant in hydrocarbon fuels and are generally present in substantially higher concentrations than nitrogen contaminants. Johnson, Fink, and Nixon (5) and Thompson e t al. (74: 75) report studies of the amounts of gum and sludge formed upon heating fuels containing small amounts of various sulfur compounds under conditions in which oxygen has access to the fuel. The results VOL. 4
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117
of the two groups differed somewhat, at least in part because of differences in the fuels and method of test. In the study by Johnson, Fink, and Nixon, the amounts of gum formed in the fuel were greatest in the presence of polysulfides. T h e order of decreasing activity was then higher aliphatic mercaptans, thiophenol, and lower aliphatic mercaptans, while "other" sulfur compounds were practically inert. In Thompson's work, thiophenol was reported to be particularly effective in forming sludge, followed by disulfides and polysulfides. Thiophenes, aliphatic mercaptans. and aliphatic sulfides were reported to show little effect. Similar studies have been reported by Davydov and Bol'shakov ( 7 ) in the 100' co 300" C. temperature range. I n the present studies. attention was focused on the effect of specific sulfur compounds on the rate of decomposition of hydrocarbons as such. No information has been previously reported on their effects on cracking rates or mechanisms of action. Previous unpublished studies on the thermal decomposition of pure saturated paraffins showed that as reaction time was increased new groups of products appeared in the following order : olefins, dienes, polyunsaturates, colored compounds, and polymers. A further increase in reaction time led to the appearance of fine carbonaceous particles in the fuel. This indicates that the fine particles are formed as the end product of a series of consecutive reactions involving the above groups of intermediates in the order given. Appearance of color always precedes particle formation in pure hydrocarbons. Particles begin to appear at a time corresponding to the decomposition of from 20 to 90% of a pure saturated hydrocarbon, depending largely upon its molecular structure but also in part upon the decomposition temperature. The technical specifications for aircraft fuel in the United States generally limit the maximum total sulfur content to a value between about 0.1 and 0.5 weight %, and mercaptan sulfur to a maximum of 0.005 weight yo. I n the Soviet Union. a maximum of 0.01 weight % mercaptan sulfur and 0.25 weight yo total sulfur is specified for TS-1 and T-2 fuels (7). T h e sulfur compounds in fuels are present in a large variety of forms Those found in straight-run fuels from the refinery include hydrogen sulfide, mercaptans. mono- and disulfides, and thiophenes (73). Limitations on sulfur content
are desired to minimize corrosion by combustion gases as well as to enhance stability during storage and during heating in aircraft fuel tanks and fuel lines prior to combustion. Experimental
Thermal decomposition rates were measured in the static test apparatus used previously to study rates of decomposition of selected saturated cyclic hydrocarbons ( 3 ) . From 1.26 to 1.5 ml. of the pure hydrocarbon or the hydrocarbon containing the sulfur contaminant was placed in a borosilicate glass tube, the quantity of hydrocarbon or mixture being adjusted to constitute in each case 40% of the tube volume a t room temperature. All samples were degassed by alternate freezing and thawing under vacuum, and the tubes were then sealed under vacuum. They were preheated for 15 to 20 minutes to 500' F. and then subjected to the reaction temperature (700', 750°, 800', or 850' F.) for from 1 to 136 hours. (An electrically heated aluminum block furnace was used to decompose six samples simultaneously. Automatic control kept the temperature within =t5' F. of the set point.) Most experimental runs were made at 800' F., although some hydrocarbons were studied at the other temperatures to investigate temperature effects. The amount of hydrocarbon reacted was determined by vapor phase chromatography, corrections being applied for the loss of gaseous products when sample tubes were opened, and for the quantity of sulfur contaminant present in the unreacted sample. Detailed procedures were those previously described (3). Each study was done with pairs of samples, the hydrocarbon containing the sulfur contaminant and the pure hydrocarbon. Possible minor temperature variations from run to run were thus eliminated, and the observed differences in rate of decomposition could be attributed solely to the contaminant. The hydrocarbons were purchased as "pure" compounds and were further purified by methods previously described ( 3 ) . Final purity was judged primarily by vapor phase chromatograms. Samples were stored in glass containers at a temperature near 0' F. I n some cases, several isomers were present, and the minimum purity was taken to be equivalent to the sum of the area of the several neighboring peaks, each presumably representing one isomer. The sulfur compounds were used as purchased without further purification. Table I lists the compounds studied. For the hydrocarbons the number of components present as indicated by the number of peaks in the chromatogram are given and also the area of the main peak as a percentage of the total.
Table 1.
Compound
n-Dodecane Undecane, 3-methylDecane, 2,9-dimethylNonane, 5-n-propylNonane, 2,2,8,8-tetramethyln-Hexadecane Cyclohexane Naphthalene, decahydroNaphthalene, decahydro-2,3-dimethylNaphthaler e, decahydro-1 -ethylNaphthalene, decahydro-l-isopropylIndan, hexahydromethyl-
Hydrocarbons and Sulfur Compounds Studied Est Lmated Vapor Phase Chromatogram Boiling No. of Minimum Main beak Point, O"F. Purity, yo area, '70 compone'nts
414 404 392 388 396 532 177,3 386 435 438 466 358
99.5 99.9 100
99.5 99.9
100
99.9+ 99.9+
99.9+ 99.9+
96.9
96.9
99.9+
99.9+
94.9
81 58.8 64.5 52.2 45
99.9+
98.7 99.9+
95.9
5 1 1 2 2 5 2 3 6
4 3 5
Source.
MRC MRC MRC MRC MRC AS EOCh DP MRC MRC MRC MRC
Physical Constants
Thiophene Benzenethiol Di-tert-butyl disulfide
Diphenyl sulfide Diphenyl disulfide
B.P. 82-84' C. B.p. 53-54' C. at 10 mm. B.P. 198-204' C. B.p. 151-53' C. at 15 mm. M.p. 59-60' C.
MBC MBC MBC EOCh EOCh
3 Co., Inc., Wilminpton, Del.; a Symbols usedfor source of sample: A S , Applied Science Laboratory, State College, Pa.; D P , E. I . du Pont de Nemours t EOCh, Eastman Organic Chemicals, Rochester, N . Y.; M B C , Matheson Coleman & Bell, JVorwood, Ohio; M R C , Boston Laboratories, .?4onsanto Research Cotp., Everett, Mass.
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Results
Hydrocarbon cracking reactions are known to be highly complex kinetically, but the decomposition reaction of a pure hydrocarbon usually can be expressed as a first-order process to a first approximation. When this holds true, the rate of decomposition of the c:ontaminated hydrocarbon generally follows approximately first-order kinetics, as illustrated by Figure 1. This shows a series of experiments carried out a t various reaction times with n-hexadecane, 5-n-propylnonane, and decahydronaphthalene, either pure or containing 2 weight 70of an added contaminant. The three hydrocarbons were chosen as representativme of straight-chain, branched-chain, and cyclic paraffins, r’zspectively. tert-Butyl disulfide and benzenethiol (also known as thiophenol or phenyl mercaptan) represent two classes of :sulfur contaminants frequently found, and sulfur compounds which have substantially different thermal decomposition rates by themselves. These studies show that the decomposition rates of n-hexadecane and decahydronaphthalene are inhibited by the sulfur compounds, while that of 5-n-propylnonane is accelerated. T h e nature of the sulfur compound has less effect on the observed behavior than the nature of the hydrocarbon. The straight lines obtained in the case of 2 weight yo thiophenol in n-hexadecane and 2 weight % tert-butyl disulfide in 5-n-propylnonane show that both the inhibition in the first system and the accelerarion in the second system can be expressed within experimental precision as a change in the
1.00
5
RlISlDENCE TIME. hrs. IO 15 20 25 30
0.90 0.80 0.70 0.60
first-order rate constant of the hydrocarbon. T h e behavior of decahydronaphthalene is different because, as developed previously ( 3 ) , the “pure” material is in fact a mixture of cis and trans isomers and during the decomposition the cis isomer is gradually converted into the more stable trans isomer. Nevertheless, a first-order rate constant can be calculated for each residence time. Although this “constant” will in fact decrease with increased reaction time, the ratio of the constants for pure and contaminated hydrocarbon, calculated for the same reaction time, is a good measure of the effect of the sulfur contaminant. Figure 2 shows the effect of other sulfur contaminants a t various concentrations and a t other temperatures on the decomposition rates of the same three hydrocarbons. The ordinate is the ratio of the first-order rate constant in the presence of the contaminant to that of the pure compound. Most of the studies were made with tert-butyl disulfide or benzenethiol. T h e latter is a much more thermally stable compound than the former and represents a structural class for which low specification limits are set. One run on each hydrocarbon was also made with thiophene, diphenyl sulfide, and diphenyl disulfide, which represent other types of sulfur compounds. T h e reac-
A
1.20
0.5
500cal. and a first-order reaction rate constant of O.dOlj8 set.-' a t a value of E K 7 ' = 24.7 (presumably for a temperature of 411' C . ) . I'his corresponds to a value of about 10 hr.-l a t 800' F. (427' C . ) a t which our studies were made and seems rather high relative to our limited quantitative data, Ivhich: hoivever. are for a much higher pressure. Elgin (2) studied the effect of reduced nickel catalysts on the decomposition of sulfur compounds and reported that mercaptans reacted most readily. then sulfides, and that thiophene was the most stable of the compounds studied-the same order of stability reported for thermal reaction. T h e authors made some brief studies of thermal decomposition rates of benzenethiol and of tert-butyl disulfide by the same sealed tube method used for pure and contaminated hydrocarbons. These reaction conditions correspond to pressures of several hundred pounds per square inch. 'Ihe studies \\.ere not sufficiently detailed to elucidate the kinetics, but on the basis of three runs a t 800' F. on benzenethiol a t about 70yc conversion we estimate a first-order reaction rate constant of about 1.0 hr.-l Two runs Lvith tert-butyl disulfide shoived complete decomposition. from Lvhich we conclude that the first-order reaction rate constant exceeded a t least 10 hr.-' and may have been much larger. The S-S bond is knolvn to be relatively weak: and the disulfides are among the most unstable of the groups of sulfur compounds considered here. T h e tert-butyl disulfide probably ranks below any of the mercaptans in the list above. Aromatic disulfides are more stable than alkyl disulfides. In another study ( 1 ) .thiophene was shown to reach a first-order reaction rate constant of 0.01 hr.-l (at low conversions) when the temperature \vas raised to 590' to 620' C. T h e values may be compared with first-order reaction rate
150" C. 200O c.
2000 c.
225-250' C. 400' C. 450' C. Stable at 500' C.
Effect of Sulfur Contaminants on Thermal Decomposition of Certain Saturated Hydrocarbons Fraction of Hjdro:arbon
Cyclohexane
Contaminant tert-Butyl disulfide Benzenethiol
2,3-Dimethyldecahydronaphthalene 1-1sopropyldecahydronaphthalene
Diphenyl disulfide tert-Butyl disulfide tert-Eutyl disulfide tert-Butyl disulfide
Methylhexahydroindan
tert-Butyl disulfide
Hydrocarbon
1-Ethyldecahydronaphthalene
wt.70
Contaminant 2.0 0.5 1.o 2.0 2.0 0.1 0.1 0.1 0.1
0.1 0.5
2.0 Benzenethiol n-Dodecane 3-Methvlundecane
Diphenyl disulfide tert-Butyl disulfide tert-Butyl disulfide
2,?-Dimethyldecane
tert-Butyl disulfide
2,2,8,8-Tetramethylnonane
tert-Butyl disulfide
0.5 1.o
2.0 0.1 0.1 0.1 0.1 0.1 0.1 0.1
Temp, F. 800 800 800 800 800 800 800 700 800 800 800 800 800 800 800 800 700 800 700 800 800
Ratio o,fJirst-orderrate constant in prrsencr of contaminant to that of pure compound.
120
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P R O C E S S DESIGN AND D E V E L O P M E N T
Cnconcerted Pure Contaminated hydrocarbon ~~
800
Time, Hr. 66 66 66 66 66
7 5 88
3 6 5.5 5.5 5.5 5.5 5.5 1.5 55 1.5 48 1.5 1.5 30
0.511 0.601 0.571 0.610 0.540 0.600 0.608 0.925 0.684
0,518 0.518 0.518 0.518 0.498 0.436 0.572 0.820 0.510 17
0.1 0.j
n
15 15 15
k Rel.0 1,021 0,7'4 0.852 0.752 0.880
0.616 0 892 0 392 0.564 0.738 1.000 0,847 0.574 0.562
0.559 0 541 0 539 0 314 0 517 0 359 0.446
0.279
0 521 0 530 0 393 0.550 0 489 0.689 0.463
0.940 0.974 1.274
1.096 1.432
2 169 1.658
cnnstants of about 0.7 hr.? for n-hexadecane, 0.6 hr.-l for propylnonane, and about 0.04 hr. -I for decahydronaphthalene, all a t 800' F. (42-' C.). T h u s of the t\vo sulfur contaminants \vith which most of our studies \\!ere made, the tert-butyl disulfide alone \vas far more unstable than any of the hydrocarbons and the thiophenol \vas comparable in stability to the t\vo paraffins but much less stable than decahydronaphthalene. 'Thiophtme is inore stable than any of the hydrocarbons studied. I h e decomposition processes of sulfur compounds are fairly complicated. .4lkyl mercaptans decompose to form varying proportions of sulfide and unsaturated hydrocarbon, plus H ? S (S). The sulfides in turn may decompose to the olefin and H,S. O n the other hand. a n olefin and H:S can easily react; espccially under pressure. to form a mercaptan and a mercaptan can add to an unsaturate to form a sulfide ( 9 ) . Disulfides form var>-ing proportions of monosulfide and mercaptan, plus I12S ( 7 0 ) . and they presumably d o not long survive under the present reaction condii.ions. I n the three runs reported: pure thiophenol was converted almost completely to diphenyl sulfidr: the remainder of the sulfur presumably forming H2S. ' l h e trrt-butyl disulfide >,vas converted completely to products of loiv molecular xveight? which ]\-ere gaseous at room temperature. T\ith all of the sulfur contaminants less stable than the hydrocarbons. H,S is presumably formed as one of the initial decomposition products and this \vould be expected to react \rith olefins or other unsaturated compounds formed by decomposition of the hydrocarbons. Hence: during a run, the sulfur r d l be largely present in the form of mercaptans. monosulfides. and H S , in proportions which may- vary considerably Ivith tiine. Discussion
Sulfur contaminants noticeably affect the rate of decomposition of saturated hydrocarbons a t concentrations as low as 0.001 to 0.01 lveight 7c, although the effects are not large even a t relatively high concentrations. Little effect of temperature was noted. It is. ho\vever, some\\-hat unexpected to find that the sulfur contaminants decrease the rate of thermal decomposition of a \vide variety of types of saturated hydrocarbons. T h e only hydrocarbons for 7,vhich the rate of decomposition was accelerated by sulfur compounds were branched-chain paraffins. T h e very limited studies with thiophene show that it had no significant effect on the rate of hydrocarbon decomposition, which is consistent with its high thermal stability. T h e thermally unstable sulfur compounds all act in the same direction-i.e.. if one causes inhibition, they all d o and the same is true for accelerating effects. However, when inhibition occurs. thiophenol is more effective than tert-butyl disulfide, but \vhen acceleration occurs, the tert-butyl disulfide is more effective than thiophenol. Lnpredicted kinetic phenomena frequently occur when mixtures of t\vo or more substances are alloived to react simultaneously. 'The rate of reaction of a n individual component of the mixture frequentl!: departs greatly from what would be expected from Bn additive rule based on the rates of reaction of the individual species alone. As a n example in another type of reaction, Russell (72) studied the oxidation rates of mixture.; of tptrahydronaphthalene and cumene upon bubbling oxygen throue;h the liquid. Tetrah)-dronaphthalene by itself \vas oxidized about t\vice. as fast as cumene. But the addition of a small amount of tetra hydronaphthalene to cumene lo\vered the over-all rate by more than a factor of 2, completely contrary to \\-hat lvould be expected by a n additive rule. Like\vise. addition of cumene to tetrahydronaphthalene raised the over-all rate slightly. 7 hese cooxidation phenomena can be
explained in terms of the relative reactivity of the free radicals formed as intermediates and corrrsponding relative emphasis upon competitive chain-carrying and chain-ending steps. Some theoretical considerations concerning co-reactions in general or so-called "cross reactions" have also been recently published by .Isepalov ( 7 6 ) . T h e reactions occurring in hydrocarbon cracking are complex, and theory cannot go very far in explaining these results. However, a n outline of the main features of the free radical reactions which probably occur here suggests the \va>- in ivhich sulfur Contaminants can either accelerate or inhibit the hydrocarbon decomposition rate. I n the absence of free radicals from other sources: the first step in hydrocarbon cracking is the rupture of a carboncarbon bond (Reaction 1). Each of the free radicals thus formed may then abstract a hydrogen atom from another hydrocarbon molecule to form the free radical, R1. \vhich decomposes to form a n olefin and a shorter radical, R ? (Reaction 3). R, may decompose further into another olefin and smaller free radical or the chain may be transferred by Reaction 4. Chains can be terminated by inactivation of a free radical on the \\all (Reaction 5 ) or by the combination of t\vo free radicals, as indicated by Reactions 6, 7, and 8. I n theor>-. the order of the reaction will vary depending upon the predominant chain-ending step. Reactions 5 and 6 are consistent lvith a n over-all first-order process. Reaction 7 \\ith halforder, and Reaction 8 \vith 3 '2-order. HoLvever, the order is not knoum here to sufficient precision or the kinetics with sufficient certitude to use this as a method of distinguishing bet\veen alternative chain-ending possibilities. hlost sulfur compounds \vi11 decompose more rapidly than the hydrocarbon, forming a n organosulfur radical \vhich can then initiate a chain by hydrogen abstraction (Reaction 2). T h e sulfur radical can also terminate chains by reactions of the type of 9 or 10.
-
Chain Initiation
R,H
k
+ R" 2R, + R'H + R"H k9 R I H + Si 4 S1H + Ri 2R1H
R'
(1)
(2)
Chain-Carrying Reactions
R, RP
+ RiH
Chain Termination R~
+ R?
(3)
R2H $- Rl
(4)
';s
01
kl
+ \Tall ---+ t5
1'
(5) ~
where R1H = original hydrocarbon R ' , R " = intermediate radicals R I = long radical SI = organosulfur radical R1 = short radical 01 = olefinic product R2H = paraffinic product TVhether the presence of sulfur contaminants causes acceleration or inhibition of the decomposition rate of the hydrcVOL.
4
NO. 1
JANUARY
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121
carbon depends upon the relative magnitude of the rates of these individual reactions. Consideration of some simplified limiting cases shows some of the conditions which can lead to one or the other. We assume in the following that the chains are of appreciable length, so that the rate of reaction, r , is approximately given by : r = k3(R1) = ka(RJ(R1H)
(11)
Inhibition by sulfur contaminants can occur if the organosulfur free radicals act primarily to terminate chains by Reaction 9 or 10 rather than initiating chains by Reaction 2. Assuming initiation primarily by Reaction 1 and chain termination preferentially by Reaction 9 :
Since the rates of chain initiation and chain termination are equal 2ki(R1H) = ks(Ri)(Si) and
For the alternative possibility of chain termination by Reaction
In both of these simplified cases, the reaction rate \vould be independent of the concentration of S1 radicals, bvhich is not in accord with the experimental data. I t is ,plausible that the organosulfur radicals do in fact participate in both initiation .and termination reactions, and this .could be incorporated into a mathematical framebvork which provides for the effect of organosulfur concentration by allowing, for example, for different reactivities for different organosulfur radicals, which are undoubtedly present in some variety. However, there is little evidence to suggest lvhich of several alternative schemes is the more likely. The fact that the relative efficacy of benzenethiol and tert-butyl disulfide reverses when they cause acceleration rather than inhibition may well also be associated with a difference between the relative reactivities of the two types of organosulfur free radicals formed with respect to chain-initiating’and chain-ending steps. But there is no obvious reason why the reaction rates of 5-npropylnonane and of the other branched-chain paraffins are accelerated by sulfur contaminantswhereas those of the straightchain paraffins are inhibited. Several assumptions have been made for mathematical tractability to simplify the real situation and all the above models are intended to serve only as a broad framework within which to view the experimental results.
10:
r =
2kikr (RiH)’ kio (Si)
Acknowledgment
(13)
Both Equations 12 and 13 are consistent with the observed increase in inhibition with increasing concentration of the sulfur contaminant, but Equation 13 indicates a second-order relationship with respect to the hydrocarbon, which is unlikely. Acceleration by sulfur contaminants can occur if free radical formation by Reaction 2 is the predominating initiating step and chain termination involves only hydrocarbon-free radicals. For example, if chain initiation is by Reaction 2 and chain termination by Reaction 5 we obtain k2k3
r = - (R1H)(Sd ks
(14)
which is a first-order reaction with respect to the hydrocarbon, promoted by increasing concentrations of the organosulfur radical. If chain termination by Reaction 6 is assumed, one obtains -I
Consider also the case in which both chain formation (Equation 2) and chain termination (Equations 9 and 10) are accelerated by organosulfur radicals. If Reactions 2 and 9 are chosen, the result is
The authors acknowledge the contributions of J. H. Cornell and Ralph Kafesjian to the experimental work. literature Cited
(1) Davydov, P. I., Bol’shakov, G. F., Khim. i Tekhnol. Toplzc Masel, No. 5 , 48 (1951); No. 10, 35 (1960). (2) Elgin, J. C., Ind. Eng. Chem. 22, 1290 (1930). (3) Fabuss, B. M., Kafesiian, R., Smith, J. O., Satterfield, C. N., ’IND.ENG.CHEM.,P R O ~ E DESIGN SS DEVELOP., 3, 248 (1964) (4) Johns, I. B., McElhill, E. A , , Smith, J. O., J . Chem. Eng. Data 7. 277 11962). (5) ’Johnion, C . R., Fink, D. F., Nixon, A . C., Ind. Eng. Chem. 46, 2166 (1954). (6) Malisoff, W. M., Marks, E. M., Ibzd., 23, 1114 (1931); 25, 780 (1933). ( 7 ) Paushkin. Ya. M.. “Chemical ComDosition and Prouerties of Fuels for Je’t Propulsion,” Pergamon Pkess, New York, f962. (8) Reid, E. E., “Organic Chemistry of Bivalent Sulfur,” Vol. I, p. 111, Chemical Pub. Co., New York, 1958. (9) Ibzd.,Vol. 11, p. 60, 1960. (10) Ibid., Vol. 111, p. 370, 1960. (11) Rudenko, M. G., Gromova, V. N., Dokl. Akad. *\‘auk SSSR 81,207 (1951) ; C.A.46,7515. (12) Russell, G., J . A m . Chem. SOC.7 7 , 4583 (1955). (13) Sachanen, A. N., “Conversion of Petroleum,“ p. 96. Reinhold, New York, 1940. (14) Thompson, R. B., Chenicek, J. A,, Druge, L. W., Symon, T., Ind. Eng. Chem. 43, 935 (1951). (15) Thompson, R. B., Druge, L. W., Chenicek, J. A.: I6id., 41, 2715 (1949). (16) Tsepalov, V. F., Zhur. Fiz. Khim. 35, 1086, 1443, 1691 (1961). \
I
RECEIVED for review .4pril 13, 1964 ACCEPTEDJuly 7, 1964 and for Reactions 2 and 10
kzkr
r = - (RIH)a kl0
122
l & E C PROCESS D E S I G N A N D DEVELOPMENT
Work performed under the direction of Air Force Aero Propulsion Laboratory, Research and Technology Division, [%‘right-Patterson Air Force Base, Ohio, on Contract AF33(616)-7845.
