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Pyrolysis of Polycyclic Perhydroarenes. 1. 9-n-Dodecylperhydroanthracene Roger E. Humburg and Phillip E. Savage* Department of Chemical Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136
9-n-Dodecylperhydroanthracene (DDPA), a prototypical long-chain, n-alkylnaphthene, was pyrolyzed neat and in benzene at temperatures between 400 and 450 °C. The global reaction order for the disappearance kinetics was 1.05 ( 0.23, which was taken to be first order in subsequent analyses. The first-order Arrhenius parameters were [log10 A (s-1), E (kcal/mol)] ) [10.5 ( 1.9, 44.7 ( 6.1]. All of the reported uncertainties are 95% confidence intervals. The major primary reaction products were dodecahydroanthracene plus n-dodecane, perhydroanthracene plus 1-dodecene, and methyleneperhydroanthracene plus n-undecane. These six products accounted for about 35% of the reacted DDPA at moderately low conversions. The balance of the DDPA formed numerous primary products such as alkanes, alkenes, and substituted perhydroanthracenes, the individual yields of which were very low. Secondary reactions included ring opening, which led to the formation of substituted tetralins and naphthalenes, and dehydrogenation, which led to octahydroanthracene, tetrahydroanthracene, and anthracene. The primary product spectrum can be accounted for by viewing DDPA pyrolysis as proceeding through four parallel free-radical chain reactions. Three of these parallel chains lead to the three sets of major primary products, and the fourth chain leads to the minor products. Introduction Central to the development of molecule-based approaches for modeling the reactions of heavy oils and coals (e.g., Gray, 1990; Neurock et al., 1990; Quann and Jaffe, 1992; Shinn, 1992; Savage and Klein, 1989) is a knowledge of the reaction pathways and kinetics for the different structural elements in these materials and in their process-derived products. This knowledge can be obtained from studies of the reactions of model compounds that mimic the structural features of the more complex material. One of the key structural features of heavy oils and asphaltenes is n-alkyl chains on the periphery of polycyclic moieties. Thermal reactions play an important role in many of the processes used to upgrade and refine heavy hydrocarbon resources. Experimental studies repeatedly show that thermal reactions can control the product yields and the reaction rates even in nominally catalytic processes (e.g., Heck and DiGuiseppi, 1994; Sanford, 1994; Szladow et al., 1989; Savage et al., 1988; Miki et al., 1983; Khorasheh et al., 1989). This dual recognition of the utility of model compounds and the significance of thermal hydrocarbon chemistry has motivated numerous model compound pyrolysis studies (Poutsma, 1990). Previous pyrolysis studies of long-chain n-alkylsubstituted compounds have been largely limited to aromatic compounds or to single-ring compounds. Polycyclic compounds, and particularly polycyclic naphthenes, with long n-alkyl chains (greater than three carbon atoms) have received much less attention. It is precisely this type of compound we consider in this series of articles. The specific compound discussed herein is 9-n-dodecylperhydroanthracene. This compound has not been pyrolyzed previously. In fact, we found no previous reports of pyrolyses of any polycyclic long-chain n-alkylnaphthenes at the temperatures of * To whom correspondence should be addressed. Phone: (313) 764-3386. FAX: (313) 763-0459. E-mail: psavage@ umich.edu.
S0888-5885(96)00059-0 CCC: $12.00
interest (350-500 °C) in fuel processing. The fully hydrogenated polycyclic compounds that have been pyrolyzed previously were either unsubstituted (e.g., Virk et al., 1979; Kopinke et al., 1993; Taylor and Rubey, 1988), or they bore short n-alkyl chains and only disappearance kinetics were reported (Fabuss et al., 1964). Although heavy hydrocarbon conversion provides the primary motivation for the research reported herein, a secondary motivation for studying alkylnaphthene pyrolysis is the renewed interest in “endothermic” jet fuels for military applications (e.g., Song et al., 1993; Edwards, 1993). High-performance jet aircraft will have higher air speeds and much higher engine temperatures than do current aircraft. These factors result in large heat loads that must be managed with the main coolant available on the aircraftsthe fuel. Such aircraft will require “endothermic” fuels, where heat is absorbed by endothermic reactions of the fuel. The main components in proposed endothermic fuels are substituted naphthenes, which can dehydrogenate to form aromatics, and n-alkanes, which can crack to lighter products. Both of these reactions are endothermic. Alkyl-substituted polycyclic naphthenes contain both long alkyl chains and naphthenic structures, so pyrolyses of these compounds could provide new insights into the thermal stability of jet fuels and the development of endothermic fuels. Experimental Section 9-n-Dodecylperhydroanthracene (DDPA) was obtained from the Thermodynamics Research Center at Texas A & M University and used as received. Gas chromatography-mass spectrometry revealed that the only detectable impurity was n-tetracosane (C24H50) at about 1.5 wt %. Isothermal pyrolysis experiments were performed in batch microreactors at 400, 425, and 450 °C both neat and in benzene. The stainless steel, tubing-bomb microreactors were fashioned from nominal 1/4 in. Swagelok tube fittings (one port connector and two caps). The reactor volume was about 0.6 mL. © 1996 American Chemical Society
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The neat pyrolysis experiments used approximately 10 mg of both the model compound and biphenyl (an internal standard). The masses of these compounds were carefully measured to within (0.1 mg. The pyrolysis experiments in benzene used 0.5 mL of a benzene solution containing varying but known amounts of the reactant and biphenyl. In these experiments, the reactant concentration was calculated as the number of moles of reactant loaded into the reactor divided by the reactor volume. In all experiments, the loaded and sealed reactors were placed in an isothermal, fluidized sand bath that had been preheated to the desired pyrolysis temperature. Upon reaching the desired batch holding time, the reactors were removed from the sand bath, and the reaction was quenched by immersing the reactors in a room-temperature water bath. The cool reactors were then opened and their contents retrieved by repeated additions of benzene. The gaseous products could not be analyzed because of their low yields and the small amount of reactant used in the experiments. The benzene-soluble pyrolysis products were analyzed by capillary-column gas chromatography (GC) using both flame ionization and mass spectrometric (MS) detectors. The GC oven temperature was set at an initial value of 60 °C for 5 min. The temperature then increased 2 °C/min to a final temperature of 240 °C, at which time the analysis was complete. Many products were positively identified by matching the retention times and mass spectra of authentic compounds to those of the peaks in the chromatograms. Other products were identified by matching their mass spectra with those stored in the GC-MS computer library or, more tentatively, by inspection of the mass spectra. Product molar yields, calculated as the number of moles of product formed divided by the number of moles of reactant initially loaded into the reactor, were obtained from the chromatographic analysis using experimentally determined detector response factors. The GC analysis of DDPA and some of its pyrolysis products was complicated because saturated polycyclic compounds can exist in different isomeric forms (e.g., cis- and trans-decalins). Indeed, we observed that perhydroanthracene and its substituted analogs exist as multiple isomers, which give multiple peaks on the GC. The response factors and molar yields for these compounds with multiple peaks were calculated using the sum of the areas of the individual peaks. The compounds with multiple GC peaks were perhydroanthracene, dodecahydroanthracene, 9-methyleneperhydroanthracene, and the reactant, 9-dodecylperhydroanthracene. Background experiments were performed to assess the effect of the small amount of oxygen (from air) in the sealed reactors and the effect of the stainless steel walls on the pyrolysis kinetics. Each set of experiments employed four reactors that were placed in a 400°C sand bath simultaneously and allowed to remain in the sand bath for 2 h. The effect of room air in the reactors was examined by loading two reactors using our standard protocol and then loading two other reactors inside a helium-filled glovebox. The mean values of the DDPA molar yield were 0.648 (loaded in air) and 0.644 (loaded in He). We tested the statistical significance of the small difference between these two means by comparing t statistics. We calculated the t statistic from the experimental results to be 0.04. To be significant at the 95% level, with two degrees of freedom, t would have to be larger than 4.30. Since the calculated t does not satisfy this condition,
there is no statistical evidence for disputing the hypothesis that the two means are equal. The effect of stainless steel was examined by adding about 12.7 mg of fine stainless-steel filings to two of the reactors before sealing them. The filings were obtained from a Swagelok port connector. The mean values of the DDPA molar yield were 0.524 (no filings) and 0.442 (filings added). The t statistic from these experimental results was 1.41. To be significant at the 95% level, however, t would have to be larger than 4.30. Since the calculated t does not satisfy this condition, there is no statistical evidence for disputing the hypothesis that the two means are equal. These background experiments also provided an opportunity to assess the run-to-run variability in the experimental data. The four reactors that were loaded following the standard protocol had a mean DDPA molar yield of 0.59 ( 0.13, where the uncertainty stated here and elsewhere in the paper is the 95% confidence interval. Thus, the relative error in the measured molar yield is about 22%. Results Table 1, which provides representative experimental results, lists the identities and molar yields of the products identified from the neat pyrolysis experiments at 400, 425, and 450 °C. Figure 1 displays the chemical structures of some of these products. Note that some of these structures are illustrative and not definitive. For example, the precise location of the double bond in dodecahydroanthracene and methyleneperhydroanthracene is not known with absolute certainty. The product spectrum listed in Table 1 includes n-alkanes, 1-alkenes, and one-, two-, and three-ring compounds bearing n-alkyl and 1-alkenyl substituents. Most of the products listed in Table 1 were positively identified. The exceptions are dodecahydroanthracene, 9-methyleneperhydroanthracene, and 9-methylperhydroanthracene. These compounds were not available commercially and their mass spectra were not stored in the GC-MS computer library, so we could not obtain authentic standards to use for comparison. Thus positive identification of these products was not possible. Our identification is based upon inspection of the mass spectra and relative retention times in the GC. For example, the peaks we identified as dodecahydroanthracenes had similar mass spectra with a strong molecular ion peak at 190 daltons. They also had GC retention times after perhydroanthracenes but before octahydroanthracene. These data are consistent with these products being dodecahydroanthracenes. Table 1 shows that the products present in molar yields of at least 1.0% from pyrolyses at low conversions (40% but tridecylcyclohexane > butylcyclohexane) is as expected for alkylnaphthenes
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since the reactivity should increase as the number of C-C and C-H bonds increases (Fabuss et al., 1964). The estimates of the Arrhenius parameters for DDPA were highly correlated, which is typically the case. Thus, the uncertainties in the parameter estimates alone are insufficient to estimate the uncertainty in the rate constant at any given temperature. The covariance of the two Arrhenius parameters, CovA,E, is also required. The uncertainty in the rate constant, ∆k, can then be calculated from the following formula, which results from the error propagation law (He´berger et al., 1987). 2
2
2
(∆kk) ) (∆AA) + (∆E RT)
-
2CovA,E ART
(2)
The uncertainties used in eq 2 can be either standard deviations or confidence limits, but the same type must be used consistently throughout. In cases such as the present one where the stated uncertainty is for log A (the parameter a in eq 1) rather than for A itself, eq 2 can be cast in a more convenient form, as given below. 2
(∆kk)
) (2.303∆a)2 +
2
(∆E RT)
-
4.606Cova,E RT
(3)
The results from our estimation of the Arrhenius parameters showed that the covariance between a and E (Cova,E) was 2.76 kcal/mol, which leads to a value of 11.5 kcal/mol at the 95% confidence level. This latter value for the covariance can be used in eq 3 along with the previously stated uncertainties for a and E at the 95% confidence level to estimate the uncertainty in the rate constant for DDPA neat pyrolysis at any temperature within the range investigated experimentally. For example, using eq 3 along with the uncertainties in a and E and the covariance given above at the 95% confidence level leads to ∆k/k ) 0.55 at 400 °C. Pyrolysis Pathways The data provided in the results section identified the most abundant reaction products and further identified pairs of products that might have formed directly from the reactant, DDPA. In this section we explore the order of appearance of the reaction products in more detail and develop a reaction network for DDPA neat pyrolysis. One can examine the initial slopes of the temporal variations of the molar yields shown in Figure 2 to discriminate between primary products, which form directly from the reactant, and those that appear later in the reaction network. The initial slope is useful because it is related to the initial selectivity of DDPA to a given product. Here we define selectivity as the number of moles of product formed divided by the number of moles of reactant that have reacted. Primary products, by definition, have a nonzero initial selectivity so they must exhibit nonzero initial slopes. Products that appear later in the reaction network have an initial selectivity of zero so they exhibit initial slopes equal to zero. Thus, an examination of the initial slopes in Figure 2 provides discrimination between primary products and those that appear later in the reaction network. Figure 2a shows that the initial slopes for dodecane, dodecahydroanthracene, perhydroanthracene, and 1-dodecene are all nonzero. Thus each of these four is a primary product formed directly from DDPA. Addition-
Figure 4. Reaction network for DDPA neat pyrolysis.
ally, the initial slopes for dodecane and dodecahydroanthracene are nearly equal, which is consistent with this product pair being formed in the same reaction step. A similar equality of initial slopes is evident for perhydroanthracene and 1-dodecene, which is consistent with a similar conclusion of formation of this pair in the same reaction step. The nonzero initial slopes (or selectivities) for n-undecane and 9-methyleneperhydroanthracene evident upon inspection of Figure 2b lead us to conclude that these two are also primary products. The initial slopes for n-decane and 1-undecene are also nonzero. Therefore, these minor products are primary products that arise directly from the reactant. We estimate that the sum of the initial selectivities for the six major primary products accounts for about 35% of the DDPA that reacts. The remaining 65% reacted to form ndecane, 1-undecene, and the many other minor products detected. The initial selectivity for any one of these minor products was about 2-3%. Figure 2c shows that octahydroanthracene, tetrahydroanthracene, and anthracene all have initial slopes equal to zero. Thus, none of these is a primary product. Note too that the yields of these products increase with time, which is also consistent with these products being formed later in the reaction network rather than in primary reactions. The conclusions drawn from this analysis and inspection of the temporal variations of the products’ molar yields in Figure 2 lead us to offer Figure 4 as the primary reaction network for DDPA neat pyrolysis. There are four parallel primary reaction paths. These lead to dodecane plus dodecahydroanthracene, dodecene plus perhydroanthracene, undecane plus 9-methyleneperhydroanthracene, and the numerous minor products, respectively. Secondary reactions (not all are shown in Figure 4) include decomposition of the alkanes and olefins, ring opening and dehydrogenation to form alkyltetralins, and dehydrogenation of perhydro- and dodecahydroanthracene to form, successively, octahydroanthracene, tetrahydroanthracene, and finally anthracene.
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Figure 5. Parallel free-radical chain reactions for DDPA neat pyrolysis.
Reaction Mechanism Hydrocarbon pyrolysis typically proceeds through a set of reversible free-radical reactions that include homolytic dissociation, disproportionation, isomerization, β-scission, and hydrogen abstraction. The last two steps often occur together in a chain sequence. That is, a radical can abstract a hydrogen atom from a molecule to form a stable product and a new radical. This new radical can then decompose by breaking a bond β to the radical center (β-scission) to produce a stable product and regenerate the abstracting radical. If the reactant is this molecule from which hydrogen is abstracted, then the two products formed in this chain reaction are primary products. We suggest that the three pairs of major primary products shown in Figure 4 form through three such chain reactions operating in parallel. These three sets of chain reactions are displayed in Figure 5. The first chain involves abstraction of a hydrogen atom from DDPA by an n-dodecyl radical to produce a tertiary (3°) DDPA radical and n-dodecane. The 3° DDPA radical then undergoes β-scission to produce dodecahydroanthracene and regenerate the n-dodecyl radical. The second chain involves abstraction of a hydrogen atom from the β-carbon in the alkyl chain in DDPA by a perhydroanthracyl radical to produce a β-DDPA radical and perhydroanthracene. The β-DDPA radical then undergoes β-scission to produce 1-dodecene and regenerate the perhydroanthracyl radical. The third chain involves hydrogen abstraction from the 9-position in DDPA by an n-undecyl radical to produce a 3° DDPA radical and n-undecane. This 3° DDPA radical then undergoes β-scission to produce methyleneperhydroanthracene and regenerate the n-undecyl radical. That these three sets of chain reactions lead to the individual primary products present in the greatest yields is consistent with the relative strengths of the different C-C and C-H bonds in DDPA. The weakest C-H bonds in DDPA are located at 3° carbons, so these hydrogen atoms are the easiest to abstract. Thus, the first and third sets of chain reactions contain the most
favorable hydrogen abstraction steps, on a per hydrogen atom basis. The weakest C-C bond in the alkyl chain is the bond that joins the chain to the perhydroanthracene moiety. This bond joins a secondary and a tertiary carbon atom. Thus, the first and second sets of chain reactions contain the most favorable β-scission steps. It is because these three chains include the most favorable hydrogen abstraction and β-scission steps that their products formed in the highest yields during DDPA neat pyrolysis. This examination of bond energies and the chain reactions in Figure 5 is also consistent with the relative abundances of the different major primary products. Recall that dodecahydroanthracene plus n-dodecane was the product pair with the highest initial selectivity. This product pair forms in the first chain in Figure 5, wherein the weakest C-H bonds are attacked in the hydrogen abstraction step and the weakest C-C bond in the alkyl chain is broken in the β-scission step. The favorable energetics associated with both of the steps in the chain reaction lead to the products of this chain being the most abundant. n-Undecane plus 9-methyleneperhydroanthracene was the second most abundant primary product pair, followed by perhydroanthracene plus 1-dodecene. This ordering shows that the relative kinetics of the third chain in Figure 5 were faster than that of the second chain. This observation, in turn, suggests that the overall kinetics of the chain reaction are more sensitive to the kinetics of hydrogen abstraction than β-scission. The second chain leading to a major product pair, however, shows that hydrogen abstraction kinetics alone do not govern product formation. If hydrogen abstraction alone controlled product formation, then perhydroanthracene and dodecene would be present in the same yield as the minor products because abstraction of the β-hydrogen in the alkyl chain is no more likely than abstraction of any of the other secondary hydrogen atoms. What makes the β-DDPA radical unique, however, is that it can decompose through the most rapid β-scission step available to any of the DDPA alkyl radicals. All of the non-β-DDPA radicals must break a stronger alkyl C-C bond to decompose, so β-scission is slower and these DDPA radicals enjoy longer lives. This longer lifetime provides an opportunity for some of these non-β-DDPA radicals to abstract hydrogen rather than to decompose by β-scission. This hydrogen abstraction could be intermolecular or intramolecular via 1,5- or 1,4hydrogen shifts. On some occasions, it is the β-hydrogen in DDPA that will be abstracted by the non-β-radicals. The net effect of this activity is a transformation of nonβ-DDPA radicals into β-DDPA radicals. The β-radicals can then decompose to form perhydroanthracene and 1-dodecene. This chain transfer activity is the reason that perhydroanthracene and 1-dodecene appear in higher yields than do the other products that arise from decomposition of DDPA radicals with the radical site along the alkyl chain. In closing, we note that there is another 3° C-H bond in DDPA, but abstraction of these 3° hydrogen atoms apparently did not lead to any major products. As shown in Figure 6, abstraction of these hydrogen atoms produces a radical that can undergo β-scission to break a C-C bond in one of the rings. The final product from this chain would be a two-ring compound with two or three substituents, and it would have precisely the same molecular weight as the reactant. We examined the chromatograms and the mass spectra of the peaks that eluted near the reactant, but we found no evidence of the formation of products of this type. One way that
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Literature Cited
Figure 6. Free-radical chain reaction with favorable bond energetics but leading to a product that was not observed experimentally.
the absence of these products can be rationalized mechanistically is if the reverse of the β-scission step in Figure 6 (radical addition to a double bond) is more rapid than the competing hydrogen abstraction step. The reverse of β-scission might occur for the radical in Figure 6 because the double bond and the radical center are within the same molecule and hence remain in close proximity. The three sets of chain reactions in Figure 5, on the other hand, all involve β-scission steps that result in the double bond and the radical being on two separate molecules that can part company. Summary and Conclusions This paper has presented the first study of the pyrolysis of a long-chain, polycyclic n-alkylperhydroarene at fuel processing temperatures. The most abundant primary products from DDPA pyrolysis at low conversions were dodecahydroanthracene plus n-dodecane, perhydroanthracene plus 1-dodecene, and methyleneperhydroanthracene plus n-undecane. Thus, the major primary reactions involve cleavage of the alkyl chain at or near the ring. Products present in high yields only at higher conversions included alkylsubstituted tetralins and naphthalenes, and octahydroanthracene, tetrahydroanthracene, and anthracene. Consequently, we conclude that ring-opening, dehydrogenation, and aromatization reactions also occur, but they follow the primary dealkylation reactions. The identities and relative abundances of the primary products are fully consistent with DDPA pyrolysis proceeding via a free-radical chain mechanism comprising four parallel chain reactions. The free-radical chain carriers can also participate in chain transfer reactions. The disappearance kinetics for DDPA pyrolysis appear to follow a first-order rate law, within the accuracy of the experimental data, with [log10 A (s-1), E (kcal/mol)] ) [10.5 ( 1.9, 44.7 ( 6.1]. Acknowledgment This work was supported, in part, by the Exxon Education Foundation. Nomenclature a ) log10 of the Arrhenius preexponential factor A ) Arrhenius preexponential factor E ) Arrhenius activation energy k ) reaction rate constant R ) gas constant t ) time, t statistic T ) absolute temperature Covi,j ) covariance of parameters i and j
Bhore, N. A.; Klein, M. T.; Bischoff, K. B. The Delplot Technique: A New Method for Reaction Pathway Analysis. Ind. Eng. Chem. Res. 1990, 29, 313. Edwards, T. USAF Supercritical Hydrocarbon Fuels Interests. Presented at the Thirty-First Aerospace Sciences Meeting, Reno, NV, January 1993; paper AIAA 93-0807. Fabuss, B. M.; Kafesjian, R.; Smith, J. O.; Satterfield, C. N. Thermal Decomposition Rates of Saturated Cyclic Hydrocarbons. Ind. Eng. Chem. Process Des. Dev. 1964, 3, 248. Gray, M. R. Lumped Kinetics of Structural Groups: Hydrotreating of Heavy Distillate. Ind. Eng. Chem. Res. 1990, 29, 505. He´berger, K.; Keme´ny, S.; Vido´czy, T. On the Errors of Arrhenius Parameters and Estimated Rate Constant Values. Int. J. Chem. Kinet. 1987, 19, 171. Heck, R. H.; DiGuiseppi, F. T. Kinetic Effects in Resid Hydrocracking. Energy Fuels 1994, 8, 557. Khorasheh, F.; Rangwala, H. A.; Gray, M. R.; Dalla Lana, I. G. Interactions Between Thermal and Catalytic Reactions in Mild Hydrocracking of Gas Oil. Energy Fuels 1989, 3, 716. Kopinke, F.; Zimmermann, G.; Reyniers, G. C.; Froment, G. F. Relative Rates of Coke Formation from Hydrocarbons in Steam Cracking of Naphtha 2. Paraffins, Naphthenes, Mono-, Di- and Cycloolefins, and Acetylenes. Ind. Eng. Chem. Res. 1993, 32, 56. Miki, Y.; Tamadaya, S.; Oba, M.; Sugimoto, Y. Role of Catalyst in Hydrocracking of Heavy Oil. J. Catal. 1983, 83, 371. Neurock, M., Libanati, C.; Nigam, A.; Klein, M. T. Monte Carlo Simulation of Complex Reaction Systems: Molecular Structure and Reactivity in Modelling Heavy Oils. Chem. Eng. Sci. 1990, 45, 2083. Poutsma, M. L. Free-Radical Thermolysis and Hydrogenolysis of Model Hydrocarbons Relevant to Processing of Coal. Energy Fuels 1990, 4, 113. Quann, R. J.; Jaffe, S. B. Structure-Oriented Lumping: Describing the Chemistry of Complex Hydrocarbon Mixtures. Ind. Eng. Chem. Res. 1992, 31, 2483. Sanford, E. C. Molecular Approach to Understanding Residuum Conversion. Ind. Eng. Chem. Res. 1994, 33, 109. Savage, P. E.; Klein, M. T. Asphaltene Reaction Pathways: 4. Pyrolysis of Tridecylcyclohexane and 2-Ethyltetralin. Ind. Eng. Chem. Res. 1988, 27, 1348. Savage, P. E.; Klein, M. T. Asphaltene Reaction Pathways: 5. Chemical and Mathematical Modeling. Chem. Eng. Sci. 1989, 44, 393. Savage, P. E.; Smith, M. A. Kinetics of Acetic Acid Oxidation in Supercritical Water. Environ. Sci. Technol. 1995, 29, 216. Savage, P. E.; Klein, M. T.; Kukes, S. G. Asphaltene Reaction Pathways 3. Effect of Reaction Environment. Energy Fuels 1988, 2, 619. Shinn, J. H. Molecular Model of Reforming Chemistry at Reformulated Gasoline Conditions. Prepr. Pap.sAm. Chem. Soc., Div. Fuel Chem. 1992, 37, 50. Song, C.; Eser, S.; Schobert, H. H.; Hatcher, P. G. Pyrolytic Degradation Studies of a Coal-Derived and a Petroleum Derived Aviation Jet Fuel. Energy Fuels 1993, 7, 234. Szladow, A. J.; Chan, R. K.; Fouda, S.; Kelley, J. F. Kinetics of Heavy Oil/Coal Coprocessing. Energy Fuels 1989, 3, 136. Taylor, P. H.; Rubey, W. A. Evaluation of the Gas-Phase Thermal Decomposition Behavior of Future Jet Fuels. Energy Fuels 1988, 2, 723. Virk, P. S.; Korosi, A.; Woebcke, H. N. Pyrolysis of Unsubstituted Mono-, Di-, and Tricycloalkanes. In ACS Advances in Chemistry Series; Oblad, A. G., Davis, H. G., Eddinger, R. T., Eds.; American Chemical Society: Washington, DC, 1979; Vol. 183, p 67.
Received for review January 31, 1996 Revised manuscript received March 27, 1996 Accepted March 27, 1996X IE9600598 X Abstract published in Advance ACS Abstracts, June 1, 1996.
