33 1
Ind. Eng. Chem. Prod, Res. Dev, 1983, 22, 331-335
Validity of the EACN Concept for Surfactant Solutions Containing Lignosulfonates John Margeson, Vladlmlr Hornof, and Graham Neale' Chemical Engineering Department, University of otlawa, Ottawa, Ontario, K1N 984 Canada
The interfacial tension behavior between hydrocarbons and surfactant solutions (containing petroleum sulfonate, lignosulfonate, and sodium chloride) was studied. In particular, the validity of the Equivalent Alkane Carbon Number (EACN) concept was explored for mixed-surfactant solutions containing lignosulfonates. The lignosulfonate employed was found to Interact synergistically with the petroleum sulfonate to produce ultra-low interfacial tensions (< mN/m) against oil phases. These interfacial tensions were measured for both single-component hydrocarbons and binary mixtures thereof. From the results obtained, it may be concluded that the EACN concept remains valid
for surfactant solutions containing lignosulfonates.
Introduction Surfactant Flooding of Petroleum Reservoirs. As a result of recent oil shortages and escalating prices of petroleum products, enhanced oil recovery (EOR) schemes are now becoming more necessary and more feasible. Such schemes are employed once an oil reservoir has stopped producing oil under its own incipient pressure. One of the more popular ways of achieving enhanced recovery of oil is by means of surfactant, or micellar, flooding (Gogarty and Tosch, 1968; Healy and Reed, 1977). This technique involves contacting the oil with an aqueous surfactant solution which is capable of producing an ultra-low interfacial tension against the oil. This leads to a lowering of capillary forces within the reservoir rock matrix, thereby allowing the oil to be displaced more easily. In addition, oil is usually solubilized to some extent into the micelles of the surfactant, which also tends to increase oil recovery. A considerable amount of research on surfactant flooding has already been performed using a class of surfactants known as petroleum sulfonates, which are particularly adept at producing ultra-low interfacial tensions against crude oil (Puig et al., 1979). However, since petroleum sulfonates are themselves derived from petroleum they tend to be expensive, and will become increasingly so in the future. Use of Lignosulfonates. The distinguishing feature of the present work is that a commercial lignosulfonate is employed as a low-cost substitute for part of the expensive petroleum sulfonate (relatively little work has been performed to date using mixtures of petroleum sulfonates with other materials). Lignosulfonates are water-soluble, anionic, surface active derivatives of lignin produced from the sulfite liquors generated during the sulfite process of wood pulping, and they are currently about one-third the price of petroleum sulfonates. In aqueous solution, lignosulfonates behave as quite strong electrolytes. More extensive details concerning the structure, characteristics and properties of lignosulfonates have previously been presented by Bansal et al. (1979) and Neale et al. (1981). Although lignosulfonates possess surface active properties in their own right, they do not exhibit ultra-low interfacial tensions against oil when employed alone in aqueous solution (Bansal et al., 1979). However, when certain lignosulfonates are employed in admixture with certain petroleum sulfonates, it has been found possible to replace up to 50% of the required petroleum sulfonate and still produce ultra-low interfacial tensions, suggesting that such mixtures may have great potential in EOR operations (Neale et al., 1981; Hornof et al., 1981; Son et al., 0196-4321/83/1222-0331$01.50/0
1982). The present authors feel that future work on these systems, and on other mixed surfactant systems, would be simplified if certain empirical relations originally developed for petroleum sulfonate systems were found to apply to these mixed surfactant systems also. The EACN Concept. It is now accepted that the mechanisms involved in enhanced oil recovery processes are extremely complex and that the optimum composition of a displacing surfactant solution has to be determined in the laboratory for each prospective oil reservoir, with due consideration being given to the nature of the reservoir fluids, temperature, pressure, rock structure, etc. Recent work by Cayias et al. (1976) and Wade et al. (1977) has produced a model capable of relating the suitability of any particular surfactant system to any given crude oil. These workers observed similarities in tha interfacial tension behavior of aqueous petroleum sulfonate solutions (against various homologous series of organic materials), which led them to postulate the Equivalent Alkane Carbon Number (EACN) concept for pure hydrocarbons and their mixtures. On the basis of this concept a numerical value is assigned to each pure hydrocarbon solely on the basis of its molecular structure. Thus: for n-alkanes, EACN = number of carbon units; for nalkylcyclohexanes, EACN = number of carbon units in alkyl side chain, plus four; for n-alkylbenzenes, EACN = number of carbon units in alkyl side chain. For example, heptane, propylcyclohexane, and heptylbenzene each possess an EACN of 7. For mixtures of organic species the EACN is determined from the equation n
EACN = Cxi(EACN)i i=l
where x i and (EACN)i are the mole fraction and EACN of the ith component, respectively. It should be noted that the EACN concept asserts that the EACN of a given mixture of oils is an inherent characteristic of the mixture in question and is independent of the surfactant solution employed. Using the EACN parameter, the interfacial tension data of Cayias et al. (1977) for two homologous series has been reproduced here in Figure 1. It will be noted that the interfacial tension passes through a sharp minimum with respect to EACN for each homologous series. EACN Corresponding to Minimum Interfacial Tension (Nmin).Cash et al. (1977) observed that the minimum interfacial tension for a given surfactant solution occurred at the same EACN, independent of the composition of the oil phase. For example, if the minimum in0 1983 American Chemical Society
332 Ind. Eng. Chem. Prod. Res. Dev., Vol. 22, No. 2, 1983
to become established, could certainly never be achieved). 0 n- ALKANES n- ALKYLBENZENES
-
I
I
xi'/
E
EACN
Figure 1. Interfacial tensions of two homologous series of hydrocarbons against a surfactant solution containing 0.2% Witco 10-80 petroleum sulfonate and 1.0% NaCl (after Cayias et al., 1977).
terfacial tension when using alkanes was found to occur against heptane, then for binary solutions of pentane and decane the minimum interfacial tension would occur against that solution having the same EACN as heptane (Le., 7). The EACN a t which this minimum occurs is defined to be the "Nmin value" of the surfactant. This concept is very useful because, given an oil of known values EACN, those surfactants possessing similar Nmin can be screened out as the ones most likely to exhibit ultra-low interfacial tensions against the oil in question, and consequently to be the most effective ones in a surfactant flooding operation.
Experimental Section Materials Employed. The petroleum sulfonate used throughout this work was Petrostep 420 (manufactured by Stepan Chemical Co., Northfield, IL), a tarry material which can be dissolved by successive leachings with hot water. The lignosulfonate employed was Marasperse C-21 (manufactured by American Can Co., Greenwich, CT), a dry brown powder which is completely soluble in water. Detailed specifications of the above two products have been provided by Son et al. (1982) and therefore are not repeated here. In common with the surfactant mixtures employed by most other workers in this field, all solutions used in the present work contained sodium chloride, which simulates the electrolyte present in the aqueous fluids found in most real petroleum reservoirs. The hydrocarbons employed included the alkanes from pentane to decane, plus cyclohexane and p-xylene, and all were of 99%+ purity. Distilled water was used in all preparations. Procedures Adopted. Stock solutions of Petrostep 420, Marasperse C-21, and NaCl were made up using distilled water and the desired mixed-surfactant solutions were made by dilution. In making up these solutions the NaCl was always added last, in case order-of-mixing effects were significant. To prepare a sample for an interfacial tension measurement, about 10 mL of the surfactant solution was poured into a test tube. On top of this, 2 mL of organic phase was carefully introduced, without any mixing, and causing as little disturbance as possible. The tube was then capped and left overnight to equilibrate. This amount of equilibration naturally does not allow time for mutual saturation to occur, but it does permit a pseudo-equilibrium to become established, such as would likely occur in a real dynamic displacement process (in such a process a true thermodynamic equilibrium, which takes several days
The interfacial tension between the oil and aqueous phases was measured by a University of Texas Spinning Drop Interfacial Tensiometer (Model 300) using the procedure recommended by Cayias et al. (1975). The temperature was maintained a t 25.0 f 0.3 OC during all measurements by blowing cooled air over the spinning shaft. The loaded sample tubes were spun for periods of 3 to 6 h a t speeds ranging from 2700 to 6000 rpm. The widths of the spinning oil droplets were measured at 30min intervals, until three consecutive width readings which differed by less than 0.001 cm were obtained. The corresponding liquid densities were determined using an Anton Parr digital densitometer at 25.0 f 0.2 OC using dry air and distilled water as the calibration standards.
Results and Discussion Concentrated Surfactant Solutions. The initial surfactant mixture selected for study was 2.5% Petrostep 420,2.0% Marasperse C-21, and 1.5% NaC1. This mixture was chosen because Hornof et al. (1981) had previously found that similar mixtures were capable of generating ultra-low interfacial tensions against various oils, and most notably against heptane. Heptane was therefore chosen for the present study, and ultra-low interfacial tensions were indeed produced, although the data reproducibility was rather poor. This lack of satisfactory reproducibility is believed to be due in part to the phase instability of the surfactant formulation employed. For solutions containing 2.5% Petrostep 420 and 1.5% NaCl the phase stability is closely related to the concentration of Marasperse C-21. Thus, at concentrations above 1.0% Marasperse C-21, the surfactant solution readily separates into two layers: a clear, brown upper layer and an opaque, brown lower layer containing the settled surfactant. At lower concentrations of Marasperse C-21 the surfactant solution remains stable for several days. These observations are consistent with the findings of Shah et al. (1977) that at low concentrations the micelles are isotropic and spherical. With increasing surfactant concentration anisotropic liquid crystalline structures appear. The appearance of such aggregates results in changes in the optical properties as well as in the electrical and rheological properties of the surfactant systems. Although optical measurements were not performed in this work, the rheology of mixed surfactant systems similar to those studied here does appear to indicate the presence of liquid crystalline structures (Neale et al., 1981). The phase behavior characteristics of mixed surfactant solutions containing lignosulfonate and petroleum sulfonate have been described in detail elsewhere (Son et al., 1982). In an attempt to improve the phase stability of the surfactant solution, as well as the data reproducibility, the present investigation was continued using considerably lower surfactant concentrations (which were still capable of generating ultra-low interfacial tensions). Reduction of Surfactant Concentrations. The first step taken in this direction was to hold the concentrations of Petrostep 420 and NaCl at 2.5% and 1.5%, respectively, and to progressivelylower the concentration of Marasperse C-21 to determine to what value it could be reduced before the interfacial tension (for heptane) started to increase appreciably. The results are shown in Figure 2, in which it can be seen that down to about 0.5% Marasperse C-21 the interfacial tension is effectively constant, but below this value it increases rapidly. It was not considered desirable to select a concentration which was within the range in which interfacial tension is very sensitive to changes in concentration, so 0.6% Marasperse C-21 was arbitrarily
Ind. Eng. Chem. Prod. Res. Dev., Vol. 22, No. 2, 1983 333
WT.% OF ADDITIVE
Figure 2. Dependence of interfacial tension of heptane on concentration of additive, for surfactant solutions containing 2.5% PeCaCI,; (0) trostep 420 and 1.5% NaCl: ( 0 )Marasperse C-21; (0) additional NaCl.
was 0.2% Petrostep 420, 0.048% Marasperse C-21, and 1.5% NaC1. This mixture showed good phase stability for a month or so, but it did separate out eventually. Son et al. (1982) discuss in detail the phase stability of systems with comparable surfactant concentrations but differing slightly in that 1-butanol was present as a co-surfactant. Using an equilibration time of about 10 days, Son et al. report that the aqueous surfactant phase separates into various layers. This complicating phenomenon was not evident in the present study, probably due to the shorter equilibration time adopted. The data reproducibility was much better when using the dilute surfactant mixture. For example, at the lowest interfacial tensions measured, the data variation was typically within a factor of 2, which is quite normal for these ultra-low tensions mN/m). Since the problems associated with the concentrated surfactant solutions (i.e., phase instability and data irreproducibility) had been eliminated, the dilute solution was adopted throughout the remaining experiments. Synergistic Effect of Lignosulfonate. A number of auxiliary experiments were carried out to confirm whether the dramatic lowering of interfacial tension obtained with lignosulfonate is due to a true synergistic interaction with the petroleum sulfonate, or is merely due to the effect of the additional Ca2+and Na+ ions present in the Marasperse C-21 lignosulfonate, which could conceivably move the surfactant system closer toward an optimal salinity (n.b.: lignosulfonates act as quite strong electrolytes in aqueous solution, having conductivities about 10 times lower than NaCl solutions of comparable concentration). To achieve the above goal, experiments were performed in which the lignosulfonate concentration in the mixed surfactant solutions was replaced by an equal concentration of pure NaC1, or pure CaC12. The data obtained (Figure 2) indicate that the addition of Na+ ions produces a moderate lowering of interfacial tension, but not nearly as much as that produced by the lignosulfonate. The addition of Ca2+is actually accompanied by an increase in interfacial tension, due to the precipitation of the active Petrostep 420 which occurs at higher Ca2+ion concentrations. Clearly, the enhanced lowering effect obtained with the lignosulfonate cannot be simulated by merely adding additional cations instead. The available evidence therefore demonstrates, fairly conclusively, that the ultra-low interfacial tensions observed are due to a synergistic interaction between the lignosulfonate and the petroleum sulfonate. The observations made above for high surfactant concentrations are entirely consistent with those made by Son et al. (1982) for low concentrations. Interfacial Tensions against Single-Component Organics. The first step toward establishing the validity of the EACN concept for mixed-surfactant solutions was to obtain interfacial tensions for the dilute surfactant mixture against various organic phases consisting of one component only. The results obtained are shown in Figure 4 and they exhibit similar trends to those displayed in Figure 1. In both cases the interfacial tension passes through a minimum with respect to EACN. The major difference is that the minimum in Figure 4 appears to be rather "broader" than the sharp minima in Figure 1 (although this observation is admittedly based on rather limited data). This type of behavior would be potentially beneficial in practice, because in the case of the broader curve it is not too critical that the EACN of the oil exactly match the Nmin value of the surfactant in order to secure an ultra-low interfacial tension. Provided the two are reasonably closely matched, the interfacial tension will still
' 7 16'
LK
lo"
4-2
4-1
x)
I
1
x)
WT % PETROSTEP 420
Figure 3. Dependence of interfacial tension of heptane on Petrostep without 420 concentration, for solutions containing 1.5% NaCI: (0) Marasperse C-21 present; ( 0 )with Marasperse C-21 present (concentration ratio of Petrostep 420 to Marasperse C-21 held constant at 256).
selected for further study. In the next set of experiments the ratio of Petrostep 420 to Marasperse (2-21 was fixed at 25:6 (on the basis of the preceding result) and the total concentration of surfactant was reduced. Figure 3 indicates that the petroleum sulfonate concentration can be reduced to about 0.1% without a marked increase in interfacial tension. Once again, in order to move away somewhat from this limiting value, a Petrostep 420 concentration of 0.2% was selected, with the proportional concentration of Marasperse C-21 being 0.048%. Figure 3 clearly demonstrates the dramatic additional lowering of interfacial tension which mixed surfactant solutions exhibit compared to solutions containing Petrostep 420 alone. It should be stressed that maintaining the ratio of Petrostep 420 to Marasperse (2-21 at 25:6 was done as a matter of convenience. It is therefore quite likely that this ratio could be further optimized for these low surfactant concentrations, with a consequent further lowering in interfacial tension. Dilute Surfactant Solutions. As noted above, the dilute surfactant mixture finally selected for further study
334
Ind. Eng. Chem. Prod. Res. Dev., Vol. 22, No. 2, 1983 -
I
c ~
16'
I
\
0
I
'
2
4
6
Q
I
Io
12
10-1 0
1
I
2
I
4
1
EACN
Figure. 4. Variation of interfacial tension of one-componentorganics for a surfactant solution containing 0.2% Petrostep 420, 0.048% Marasperse C-21, and 1.5% NaCl. The organics employed were p-xylene [EACN of 21, cyclohexane [4], pentane [5], hexane [6], heptane [ 7 ] ,octane [8], and decane [lo].
be within the ultra-low region. Conversely, if the minimum is very sharp, then minor differences between the EACN of the oil and the Nminvalue of the surfactant could drastically affect the prevailing interfacial tension. In any case, the fact that the curve does exhibit a minimum indicates that the EACN concept is equally useful for representing the interfacial tension behavior of the present mixed-surfactant solutions as it is for solutions of petroleum sulfonates alone. The possible reasons for the apparent broadening of the ultra-low interfacial tension region have not been fully explored to date. However, Son et al. (1982) found that the range of NaCl concentration which is capable of producing ultra-low interfacial tensions is also broader for these mixed surfactants than it is for comparable solutions of petroleum sulfonate alone. This broadening phenomenon is most probably related to the fact that Marasperse C-21 lignosulfonate is highly polydisperse, having a very wide molecular weight distribution. Interfacial Tensions against Binary Organic Mixtures. Having elucidated the relationship between interfacial tension and EACN for one-component organics (Figure 4),the corresponding behavior for binary organic mixtures was then studied, using the same dilute mixed surfactant solution as before. The binary pairs employed were pentane-octane, cyclohexane-decane, pentane-decane, and hexane-decane. For each binary pair the EACN was varied throughout the available range and the resultant findings are displayed in Figures 5 and 6. All four sets of data exhibit minima at approximately the same EACN as for the single-component data (i.e., at an N,,, value of about 7). However, it is interesting to note that the cyclohexane-decane system exhibits minimum interfacial tensions which are almost 10 times lower than for the three other binary mixtures. On the basis of the preceding findings, it appears that N- is effectively constant for the dilute mixed-surfactant system studied here. The minimum interfacial tensions for the four binary pairs, and for the one-component systems, all occur within the approximate EACN range of 7.0 f 0.5. On account of the "broad" nature of the minima, a variation of this magnitude (i.e., f0.5) is not likely to be critical in practice, as was discussed earlier. The data presented above confirm that the EACN concept remains valid for lignosulfonate/petroleum sulfonate surfactant mixtures. This is to be expected since, according to the concept, the EACN of a given mixture of
6
1
1
8
I
1
1
1
1
I
0
1
I
2
EACN
Figure 5. Variation of interfacial tension of binary organic mixtures for a surfactant solution containing 0.2% Petrostep 420, 0.048% Marasperse C-21, and 1.5% NaCI: (0)mixtures of pentane and octane; (0)mixtures of cyclohexane and decane; (- - -) one-component organics (from Figure 4).
16'
0
2
4
6
8
1
0
1
2
EACN
Figure 6. Variation of interfacial tension of binary organic mixtures for a surfactant solution containing 0.2% Petrostep 420, 0.048% Marasperse C-21, and 1.5% NaCl: (0)mixtures of pentane and decane; ( 0 )mixtures of hexane and derane; (- - -) one-component organics (from Figure 4).
oils is an inherent characteristic of the oil, being independent of the surfactant solution in question. Conclusions (1) The interfacial tension between a mixed-surfactant solution (containing commercial petroleum sulfonate and lignosulfonate) and various organic phases was found to be a strong function of the EACN for both single-component and binary organic mixtures. (2) For a given mixed-surfactant solution the EACN at which the minimum interfacial tension occurs (Nmh)was found to be effectively constant at about 7.0 f 0.5 for all oil systems studied. (3) The EACN concept, which was originally devised for petroleum sulfonate surfactant systems, remains valid for mixed surfactant systems containing petroleum sulfonate and lignosulfonate. Acknowledgment Financial support in the form of a Strategic Grant from the Natural Sciences and Engineering Research Council of Canada is gratefully acknowledged. Registry No. Marasperse C-21,37325-33-0; sodium chloride, 7647-14-5;pentane, 109-66-0;hexane, 110-54-3;heptane, 142-82-5; octane, 111-65-9 nonane, 111-84-2;decane, 124-18-5;cyclohexane,
Ind. Eng. Chem. Prod. Res. Dev. 1983, 22, 335-343
110-82-7;p-xylene, 106-42-3;Petrostep 420, 64104-25-2.
Literature Cited Bansal, 0. B.; Hornof, V.; Neale, G. Can. J. Chem. Eng. 1070, 5 7 , 203-210. Cash,L.; Caylas, J. L.; Fournler, 0.; MacAlllster, D.; Schares, J.; Schecter, R. S.; Wade, W. H. J. Colloid Interface Sci. 1977, 59, 39-44. Cayias, J. L.; Schecter, R. S.;Wade, W. H. ACS Symp. Ser. 1975, (8), 234-247. Caylas, J. L.; Schecter, R. S.;Wade, W. H. Sac. Pet. Eng. J. 1978, 16, 35 1-357. Cayias, J. L.; Schecter, R. S.; Wade, W. H. J. Co//oidInterface Sci. 1077, 59, 31-38. Gogarty, W. 0.; Tosch, W. C. J. Pet. Technol. 1088, 2 0 , 1407-1414. Healy, R. N.; Reed, R. L. SOC.Pet. Eng. J. 1977, 17, 129-139.
335
Hornof, V.; Neale, G.; Bourgeois, P. Can. J. Chem. Eng. 1981, 59, 554-556. Neale, G.; Hornof, V.; Chlwetelu, C. Can. J. Chem. 1981, 59, 1938-1943. Puig, J. E.; Fransls, E. I.; Davis, H. T.; Miller, W. G.; Scrlven, L. E. Soc.Pet. Eng. J . 1070, 19. 71-82. Shah, D. 0.; Bansal, V. K.; Chan, K.; Hsleh, W. C. I n “Improved Oil Recovery by Surfactant and Polymer Flooding”; Shah, D. 0.; Schectec, R. s., Ed., Academic Press: New York, 1977; pp 293-337. Son, J. E.;Neale, G. H.; Hornof, V. Can. J. Chem. Eng. 1082, 6 0 , 684-691. Wade, W. H.; Morgan, J. C.; Jacobson, J. K.; Schecter, R. S . SOC.Pet. Eng. J. 1977, 17, 122-128.
Received for review February 4, 1982 Revised manuscript received August. 11, 1982 Accepted October 23, 1982
Steam Cracking of Hydrocarbons. 6. Effect of Dibenzyl Sulfide and Dibenzyl Disulfide on Reaction Kinetics and Coking Martln Bajus and Jozef Baxa Department of Chemistry and Technology of Petroleum, Slovak Technical Unlversity, 880 37 Bratislava, Czechos/ovakia
Plet A. Leclercq’ and Jacques A. RIJks Laboratory of Instrumental Analysis, Department of Chemical Engineering, Elndhoven University of Techno/ogy, 5600 MB Eindhoven, The Netherlands
The influence of aromatic sulfides on the kinetics and selectivity of hydrocarbon conversion by steam cracking and on pyrolytic coke formation was investigated in stainless steel tubular reactors with relatively large inner surface. The rate of decomposition of heptane (at 700 ‘C,100 kPa, and a mass ratio of steam to feed 3:l) increased by 16 to 26 % , and the selectivity toward ethene decreased, if 0.1 to 1.O % mass of dibenzyl sulfide, relative to heptane, was added. Addiiion of 1% mass dibenzyl disulfide increased the decomposition rate of heptane by 8 % . Increasing amounts of the title compounds (0.1, 0.5% mass) in the feed decreased coking up to 70% in the pyrolysis of reformer raffinate at 820 O C , without steam. The decreased coking in turn caused an increased aromatic content in the liquid pyrolysis product mixtures. Based on the analytical results, obtained by capillary gas chromatography-mass spectrometry, reaction mechanisms are suggested.
Introduction The production of lower olefins by pyrolysis of hydrocarbons can be enhanced in several ways. Certain additives can decrease the required temperature of pyrolysis, enhance the rate of radical conversion, increase the flexibility of the pyrolysis process, and improve the selectivity. Presently an intensive search is going on for such compounds, both of homogeneous and heterogeneous nature. Substances which favorably influence the pyrolysis process (initiators, catalysts, activators, promotors) and compounds which suppress the formation of undesirable pyrolysis products (inhibitors, retarders, deactivators, passivators) have been investigated. Application of these chemicals in production processes is, however, often limited by their effectiveness, availability, or price. Compounds which can influence the radical process of thermal decomposition include inorganic and organic derivatives of nitrogen, oxygen, sulfur, and phosphorus. Sulfur compounds can influence the course not only of primary but also of secondary reactions, which causes considerable difficulties. Well-documented are the effects of hydrogen sulfide on the kinetics and selectivity of the
conversion of hydrocarbons (Rebick, 1981; Scacchi et al., 1970; McLean and McKenney, 1970; Large et al., 1972; Scacchi et al., 1968; Frech et al., 1976; Gousty and Martin, 1974; Hutchings et al., 1976) and on the influence of secondary reactions, proceeding on the inner surface of the pyrolysis reactor when coke is formed (Crynes and Albright, 1969; Dunkleman and Albright, 1976; Ghaly and Crynes, 1976; Albright and McConnel, 1979). Under specific pyrolysis conditions elemental sulfur, sulfur dioxide (Lang, 1967), dimethyl disulfide and methyl mercaptan (Bradshaw and Turner, 1966) have a dehydrogenation effect. Elemental sulfur (Bajus and Veself, 1980) and thiophene (Bajus et al., 1981) significantly inhibit coke formation during pyrolysis and at the same time accelerate the conversion of hydrocarbons. The search for other sulfur compounds, which could favorably influence the pyrolysis of hydrocarbons to olefins, goes on. Aromatic sulfides and disulfides, which decompose to highly stabilized radicals, come into consideration. Such compounds are dibenzyl sulfide and dibenzyl disulfide. Their influence on the kinetics of conversion and coke formation in the pyrolysis of hydrocarbons was studied in this work.
0196-4321/83/ l222-0335$0l.50/0 0 1983 American Chemical Society
