Reassessment of the Kinetic Influence of Toluene on n -Alkane Pyrolysis

3817r 2010 American Chemical Society pubs.acs.org/EF

Energy Fuels 2010, 24, 3817–3830 : DOI:10.1021/ef100253zPublished on Web 06/28/2010

Reassessment of the Kinetic Influence of Toluene on n-Alkane Pyrolysis

Fr�ed�eric Lannuzel,†,‡ Roda Bounaceur,† RaymondMichels,‡ G�erard Scacchi,† and Paul-Marie Marquaire*,†

†Laboratoire R�eactions et G�enie des Proc�ed�es, LRGP CNRS-UPR 3349, Nancy University, ENSIC, BP 20451,54001 Nancy, France, and ‡G2R CNRS-UMR 7566, Nancy University, BP 236, 54501 Vandoeuvre-l�es-Nancy, France

Received March 5, 2010. Revised Manuscript Received June 10, 2010

The inhibition effect of toluene on the kinetics of n-alkane pyrolysis has been well-known for a long time.However, most studies were performed at high-temperature-low-pressure conditions. The present studyinvestigates a wider range of experimental pressures and temperatures (from 0.001 to 700 bar and from 350to 600 �C). To account for those, a kineticmodel based on free-radical reactionswas developed. Thismodelwas tested against available literature data for the low-pressure range and against new experiments for thehigh-pressure range.Whatever the temperature and pressure, it arises that toluene has indeed an inhibitiveeffect on the pyrolysis of n-octane. This effect is explained by the formation of benzyl radicals stabilized byresonance, via hydrogen-transfer reactions, that leads to new termination reactions. However, this inhi-bition will be significantly modulated as a function of the pressure, temperature, and reaction progress,from strong to very weak. Our paper describes the mechanistic reasons for this change in the extent of theinhibition effect and proposes an integrated model for the kinetic effects of monoaromatic hydrocarbonson n-alkanes during pyrolysis.

1. Introduction

Hydrocarbon pyrolysis is of concern in a large variety ofresearch fields, such as coal liquefaction, petroleum refining,thermal evolution of crude oils in sedimentary basins, heavy-oil recovery, oil-shale retort, and thermal cracking of jet fuels.As a result, the individual thermal decomposition of hydro-carbons is a continuous subject of publications. Until now, agreat number of these works were related to the study of the

pyrolysis of aliphatic compounds1-6 and aromatic com-pounds.7-12 However, the chemical and kinetic behavior ofthese compounds in hydrocarbon mixtures remains poorlyunderstood. Work on the interactions of hydrocarbons inmixtures relates to toluene, tetralin, and their inhibiting effecton alkane pyrolysis.13-18 Burkle-Vitzthum et al.15 highlightedthe inhibition role of alkyl aromatics with a side chain com-prising more than four carbon atoms on n-alkane pyrolysis,whereas these compounds were initially expected to act asaccelerators.19

The purpose of this work is to reassess the kinetic effects oftoluene on n-alkane pyrolysis in a broad range of pressuresand temperatures (from0.001 to700barand from350 to600 �C).For low-pressure conditions, the abundant available literaturewas investigated,while forhigh-pressure conditions, newexperi-ments were conducted. Radical chemical mechanisms based

*To whom correspondence should be addressed. E-mail: [email protected].(1) Fabuss, B.M.; Smith, J. O.; Lait, R. I.; Fabuss,M. A.; Satterfield,

C. N. Kinetics of thermal cracking of paraffinic and naphthenic fuels atelevated pressures. Ind. Eng. Chem. Process Des. Dev. 1964, 3 (1), 33–37.(2) Domin�e, F. Kinetics of hexane pyrolysis at very high pressures. 1.

Experimental study. Energy Fuels 1989, 3 (1), 89–96.(3) Behar, F.; Vandenbroucke,M. Experimental determination of the

rate constants of the n-C25 thermal cracking at 120, 400, and 800 bar:Implications for high-pressure/high-temperature prospects. EnergyFuels 1996, 10 (4), 932–940.(4) Yu, J.; Eser, S. Kinetics of supercritical-phase thermal decom-

position of C10-C14 normal alkanes and their mixtures. Ind. Eng. Chem.Res. 1997, 36 (3), 585–591.(5) Dahm, K. D.; Virk, P. S.; Bounaceur, R.; Battin-Leclerc, F.;

Marquaire, P. M.; Fournet, R.; Daniau, E.; Bouchez, M. Experimentaland modelling investigation of the thermal decomposition of n-dodecane.J. Anal. Appl. Pyrolysis 2004, 71 (2), 865–881.(6) Herbinet, O.; Marquaire, P. M.; Battin-Leclerc, F.; Fournet, R.

Thermal decomposition of n-dodecane: Experiments and kinetic mode-ling. J. Anal. Appl. Pyrolysis 2007, 78 (2), 419–429.(7) Blades, H.; Blades, A. T.; Steacie, E. W. R. The kinetics of the

pyrolysis of toluene. Can. J. Chem. 1954, 32, 298–311.(8) Burkl�e-Vitzthum, V.; Michels, R.; Scacchi, G.; Marquaire, P. M.

Mechanistic modeling of the thermal cracking of decylbenzene. Appli-cation to the prediction of its thermal stability at geological tempera-tures. Ind. Eng. Chem. Res. 2003, 42 (23), 5791–5808.(9) Leininger, J. P.; Lorant, F.; Minot, C.; Behar, F. Mechanisms of

1-methylnaphthalene pyrolysis in a batch reactor. Energy Fuels 2006,20 (6), 2518–2530.(10) Pamidimukkala, K. M.; Kern, R. D.; Patel, M. R.; Wei, H. C.;

Kiefer, J. H. High-temperature pyrolysis of toluene. J. Phys. Chem. A1987, 91 (8), 2148–2154.(11) Poutsma, M. L. Fundamental reactions of free radicals relevant

to pyrolysis reactions. J. Anal. Appl. Pyrolysis 2000, 54 (1), 5–35.

(12) Savage, P. E. Mechanisms and kinetics models for hydrocarbonpyrolysis. J. Anal. Appl. Pyrolysis 2000, 54 (1), 109–126.

(13) Bounaceur, R.; Scacchi, G.; Marquaire, P. M.; Domin�e, F.;Br�evart, O.; Dessort, D.; Pradier, B. Inhibiting effect of tetralin on thepyrolytic decomposition of hexadecane. Comparison with toluene. Ind.Eng. Chem. Res. 2002, 41 (19), 4689–4701.

(14) Burkl�e-Vitzthum, V.; Michels, R.; Bounaceur, R.; Marquaire,P. M.; Scacchi, G. Experimental study and modeling of the role ofhydronaphthalenics on the thermal stability of hydrocarbons underlaboratory and geological conditions. Ind. Eng. Chem. Res. 2005,44 (24), 8972–8987.

(15) Burkl�e-Vitzthum,V.;Michels, R.; Scacchi,G.;Marquaire, P.M.;Dessort, D.; Pradier, B.; Brevart, O. Kinetic effect of alkylaromatics onthe thermal stability of hydrocarbons under geological conditions.Org.Geochem. 2004, 35 (1), 3–31.

(16) Khorasheh, F.; Gray, M. R. High-pressure thermal cracking ofn-hexadecane in tetralin. Energy Fuels 1993, 7 (6), 960–967.

(17) Khorasheh, F.; Gray, M. R. High-pressure thermal cracking ofn-hexadecane in aromatic solvents. Ind. Eng. Chem. Res. 1993, 32 (9),1864–1876.

(18) Taylor,H. S.; John, J.; Smith,O. The reactions ofmethyl radicalswith benzene, toluene, diphenyl methane and propylene. J. Chem. Phys.1940, 8, 543.

(19) Domin�e, F.; Dessort, D.; Br�evart, O. Towards a new method ofgeochemical kinetic modelling: Implications for the stability of crudeoils. Org. Geochem. 1998, 28 (9-10), 597–612.

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Energy Fuels 2010, 24, 3817–3830 : DOI:10.1021/ef100253z Lannuzel et al.

on elementary reactions were considered and allowed toconstruct a general kineticmodel able todescribe the behaviorof the toluene-n-alkane system in a large range of reactionconditions.

2. Literature Overview

2.1. Previous Low-Pressure Studies. Taylor et al. were thefirst authors to highlight the inhibiting role of toluene on thecracking of alkanes.18 Szwarc studied the pyrolysis of ethyl-benzene and used toluene as a carrier gas to stop the chainreaction induced by the CH3

• radical (reaction 1) at tempe-ratures from 615 to 745 �C and pressures of a fewmillibars.20

C6H5CH2CH3 f C6H5CH2• þ CH3• ð1Þ

C6H5CH3 þCH3• f C6H5CH2• þ CH4 ð2ÞWith the concentration of this compound being very impor-tant in the medium (toluene/ethylbenzene=50:1), the CH3

•

radicals are converted into CH4 according to reaction 2. Therate of formation of CH4 is then directly correlated to thedecomposition rate of ethylbenzene according to reaction 1,with the rates of reactions 1 and 2 being equal. This reactionknown as the “toluene carrier technique” has been thereafterextensively applied. Baronnet21 observed in experiments at512 �C that the addition of toluene very strongly decreasedthedecomposition rate of neopentane (Figure 1).Razafinarivo22

also studied the influence of toluene on n-octane pyrolysisunder inert gas at a total pressure of 1300 mbar (1.3 mbar ofn-octane and a molar toluene/octane ratio of 0.9) at 450 �C.The results for two of the principal reaction products arepresented in Figure 2. As expected, the presence of tolueneinduces a strong inhibition of the products formation by afactor higher than 3.

2.2. Previous High-Pressure Studies. The available litera-ture on the pyrolysis of the toluene-alkane binary mixtureis fairly scarce. Khorasheh et al.16 pyrolyzed a toluene-hexadecane mixture (5% alkane) at 420 �C and 139 barwithin a tubular reactor. They highlighted a moderate inhi-bition of hexadecane pyrolysis by toluene. On the basis of theexperimental data of Khorasheh et al.16 and using the theo-retical study of the acceleration or inhibition mechanisms ofchain reactions by Niclause et al.,23 Bounaceur24 proposedreaction mechanisms of alkane pyrolysis in the presence oftoluene. This allowed for a theoretical study on the influenceof various factors on the inhibiting behavior of toluene onn-alkanes. For instance, Bounaceur24 performed simulationsof amixture of n-octane and 5, 20, and 70mol%of toluene at380 �C and 700 bar with a residence time of 4 days. Figure 3shows the conversion of n-octane in these different mixtures.The model predicts that toluene considerably reduces theconversion of n-octane. The effect increases with the concen-tration of toluene.

2.3. Definition of the “Inhibition Factor” (IF). To measurethe inhibition/acceleration effect of a compound (the addi-tive) on the thermal degradation of a co-reactant, Bounaceuret al.13 as well as Burkl�e-Vitzthum et al.15 defined the IF asfollows:

IF ¼ conversion of reactant without additive

conversion of reactant with additive

IF values greater than 1 indicate an inhibition effect, whereasIF values below 1 indicate an acceleration effect, on the de-compositionrateof theco-reactant.Thus, in thecaseofFigure3,obtained by simulations, the IF of the n-octane-toluene mix-ture varies fromabout 4 to 38when the proportion of toluenerises from 5 to 70 mol % at 380 �C and 700 bar.

Burkl�e-Vitzthum et al.14,15 measured and compared the IFvalues for several mixtures between 300 and 400 �C at 700 bar.

Figure 1. Evolution of the ratio of the initial pyrolysis rate of neopentane in the presence of toluene to the initial pyrolysis rate of pure neo-pentane as a function of the toluene/neopentane ratio at 512 �C and 33 mbar (according to Baronnet21).

(20) Szwarc, M. The C-C bond energy in ethylbenzene. J. Chem.Phys. 1949, 17 (5), 431–435.(21) Baronnet, F. La Pyrolyse du Neopentane, son Inhibition et son

Autoinhibition; Facult�e des Sciences: Nancy, France, 1970.(22) Razafinarivo, N. Etude cin�etique de la pyrolyse du n-octane

induite par un hydroperoxyde. Application �a l’ �Evolution Thermique desP�etroles dans les Gisements; Institut National Polytechnique de Lorraine(INPL): Nancy, France, 2006.

(23) Niclause, M.; Martin, R.; Baronnet, F.; Scacchi, G. Etudeth�eorique d’un m�ecanisme d’acc�el�eration ou d’inhibition de r�eactionsen chaınes de d�ecomposition. Rev. Inst. Fr. Pet. 1978, 21, 1724–1760.

(24) Bounaceur, R. Mod�elisation Cin�etique de l’ �Evolution Thermiquedes P�etroles dans les Gisements; Institut National Polytechnique de Lorraine(INPL): Nancy, France, 2001.

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(i) The IF value for the 20 mol % decylbenzene-80 mol %hexadecane mixture is about 2.5. (ii) The IF value for the20 mol % tetralin-80 mol % hexadecane is about 5.

Behavior of the IF for decylbenzene and tetralin as a func-tion of the temperature and mixture composition can befound from Burkl�e-Vitzthum et al.14,15 These authors de-monstrate that IF values may evolve by two orders ofmagnitude with the temperature in a non-linear fashion. Inthe 300-400 �C and 700 bar conditions, tetralin is a morepowerful inhibitor for hexadecane cracking than decylben-zene, but at T = 200 �C, decylbenzene is a much greaterinhibitor. The IF cannot be predicted without constructionof the detailed reaction mechanisms.

3. Experimental Section

3.1. Samples. n-Octane (purity 99%) and toluene (purity99.5%) were obtained from Aldrich and Fluka, respectively,and used as received.

3.2. Confined Pyrolysis Procedure. Pyrolysis was carried outin gold cells (40 mm length, 5 mm inner diameter, and 0.5 mmthick). Gold tubes were sealed at one end, then filled with 30 mgof sample under a helium atmosphere (purity 99.9999%) toavoid the presence of oxygen, and then arc-welded at the otherend under a refrigerated nitrogen flow in order not to damagehydrocarbons. The gold cells were loaded in stainless-steel auto-claves and pressurized by a fluid up to 700 bar for temperaturesbetween330 to450 �Cfrom24h to1month.At the endofpyrolysis,

the autoclaves were rapidly (5 min) cooled to room temperaturein awater heat exchanger, so that the cooling timewas negligiblerelative to the heating time. For each experimental condition,three samples were used for quantitation as well as reproduci-bility check and one sample was used for product identification.Details of the confined pyrolysis procedure can be found inLandais et al.25 and Michels et al.26,27

3.3. Identification of Products. Gold cells were pierced, cutinto pieces, placed into a vial containing hexane, and then extrac-ted in an ultrasonic bath for 1 h. Compounds were identified bygas chromatography-mass spectrometry [HP 5890 series II gaschromatograph (GC) coupled to a HP 5971 mass spectrometer]usinga60mDB,5 J&WScientific, 0.25mminnerdiameter, 0.1mm

Figure 2. Comparison of the evolutions of the molar fraction of two of the pyrolysis products for pure n-octane and the binary mixturen-octane/toluene (1:0.9) at 450 �C and 1.3 mbar of n-octane diluted in nitrogen, with a total pressure of 1300 mbar (according to Razafinarivo22).

Figure 3. Simulated conversion evolution of n-C8 according to the residence time at 380 �C and 700 bar (according to Bounaceur24).

Table 1. Critical Pressures and Temperatures for n-Octane,

Toluene, and Argon

critical pressure (bar) critical temperature (�C)

toluene 41 318n-octane 24.8 295argon 48.7 -122

(25) Landais, P.; Michels, R.; Poty, B. Pyrolysis of organic matter incoldseal pressure autoclaves. Experimental approach and applications.J. Anal. Appl. Pyrolysis 1989, 16, 103–115.

(26) Michels, R.; Landais, P. Artificial coalification: Comparison ofconfined pyrolysis and hydrous pyrolysis. Fuel 1994, 73 (11), 1691–1696.

(27) Michels, R.; Landais, P.; Philp, R. P.; Torkelson, B. E. Influenceof pressure and the presence of water on the evolution of the residualkerogen during confined, hydrous, and high-pressure hydrous pyrolysisof Woodford shale. Energy Fuels 1995, 9 (2), 204–215.

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film, fused silica column. The temperature program was 60-160 �C at 15 �C/min followed by heating to 300 �C at 3 �C/min.

3.4. Quantitation of Products. Gold cells were pierced in avacuum line maintained at 250 �C (apparatus and procedure aredescribed by G�erard and Landais28). An aliquot of 0.5 mL wassampled online and injected through a heated transfer line into aHP 5890 series IIGCwith a 60mDB, 5 J&WScientific, 0.32mminner diameter, 0.45 μm film, fused silica column connected to aflame ionization detector (FID). The temperature program was0 �C for 1 min followed by an increase of 6 �C/min up to 300 �C.Compounds were quantitated by calibration of the FID usingcommercially available standards.

3.5. Phase State of the n-Octane/Toluene/Argon Mixture.

Before experimentally studying the pyrolysis of the n-octane-toluene mixture, it was necessary to verify the phase state of thesystem. Indeed, all reactants need to be in the same homogeneousphase, so that homogeneous kinetic formalism can apply. If itwas not the case, both co-reactants could be in twodifferent phasesand contact would be limited to the interface. In our experimentalconditions, n-octane, toluene, and argon, given their critical pres-sures and temperatures (Table 1), are in the same supercriticalstate. To test this over the experimental range, we used thePPR78 model, developed by Jaubert andMutelet,29 allowing usto predict the phase state of our ternary mixture. Figure 4 pre-sents the predictions of this model according to the temperatureand pressure for amixture constituted in equal quantity of tolueneand octane and various molar proportions of argon. The inside ofthe various envelopes of phase corresponds to a biphasic state,and the entire zone outside of these envelopes indicates a singlephase. The model shows that, for our experimental temperatures(T>350 �C), the mixture n-octane/toluene/argon is in a singlephase regardless of the argon proportion and pressure.

4. Results

4.1. Influence of the Presence of Toluene on the Conversion

of n-Octane at High Pressures.The first series of experiments

was carried out at 350 �C and 700 bar for a mixture of 10%toluene in n-octane. The kinetic effect is followed by theformation of n-pentane, one of themain products of n-octanepyrolysis. In these experimental conditions, toluene does notshow an important kinetic effect on the pyrolysis of n-octane;the inhibition factors are of the order of 1.2 at most (Figure 5).n-Octane was also pyrolyzed in the mixture with benzene, acompound for which the kinetic effect on n-octane is expec-ted to be negligible. The effects of toluene and benzene onn-octane pyrolysis are very similar (Figure 5).

In another series of experiments, the influence of the abun-dance of toluene on the cracking of n-octane at 700 bar wasstudied. Bounaceur13 showed by simulation that increasingamounts of toluene should induce a significant increase inthe inhibition effect in these conditions. Figure 6 presents theevolution of the partial pressure of n-butane as a function ofthe pyrolysis time for various molar ratios of toluene at 10, 20,30, 50, and 90%.An inhibition of the pyrolysis of n-octane by

Figure 4. Prediction of the state of phase of a ternary mixture of n-C8/toluene/argon as a function of the temperature and pressure.

Figure 5. Evolution of the partial pressure of n-pentane (a pyrolysisproduct of n-octane) as a function of the pyrolysis time for then-octane/toluene and n-octane/benzene molar mixtures at 350 �Cand 700 bar.

(28) Gerard, L.; Elie, M.; Landais, P. Analysis of confined pyrolysiseffluents by thermodesorption-multidimensional gas chromatography.J. Anal. Appl. Pyrolysis 1994, 29 (2), 137–152.(29) Jaubert, J. N.; Mutelet, F. VLE predictions with the Peng-

Robinson equation of state and temperature dependent kij calculatedthrough a group contribution method. Fluid Phase Equilib. 2004, 224 (2),285–304.

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toluene is observed but remains very low, with IF rangingbetween 1 and 1.4. On the contrary to what was predicted bythe model by Bounaceur,24 our experimental results indicatethat the amount of toluene has a very weak influence on theinhibition effect.

Our experimental results conducted at a pressure of700 bar, thus, do not present the inhibition effect of tolueneon the thermal decomposition of n-octane as predicted by theliterature.

4.2. Detailed Study of the Pyrolysis Products. 4.2.1. Puren-Octane Pyrolysis.Major pyrolysis products of n-octane aredistributed into three types (Figure 7): linear alkanes fromC1

to C6 (called alkanes-minus, alkanes lighter than the reac-tant), branched alkanes from C9, and higher homologues(called alkanes-plus).

4.2.2. Pure Toluene Pyrolysis. The main product of puretoluene pyrolysis is benzene. Other reaction products aremethane, C2 compounds, biaromatics, xylenes, and trimethyl-benzenes (Figure 8). Isomers of biaromatics were not struc-turally identified and were grouped for quantitation.

4.2.3. n-Octane/TolueneMixturePyrolysis.TheC1-C6 com-pounds are similar in proportion to those generated during thepyrolysis of pure octane. However, in contrast to the pyrolysisof pure toluene, benzene was not detected. The majority of thecompounds having a greater molecular weight than toluenecorrespond to products of cross-reactions between n-octaneand toluene.They correspond toahomologous series ofC4-C9

alkylbenzenes and methylalkylbenzenes. Compounds derivedfrom each of the two reactants are also found in lesser propor-tions: undecane, dodecane derived from n-octane and tolueneandmethylbiphenyl- andmethylbenzylphenyl-type compoundsderived from toluene (Figure 9).

5. Mechanism Construction

The pyrolysismechanismof the n-octane/toluenemixture isconstructed by taking into account the entire pyrolysismecha-nismsof the twopure compounds andadding the various cross-reactions between the major molecules and/or major radicalsproduced from each reactant. These coupling reactions mustbewritten in a systematicway, as in the case of pure compounds,by considering successively the various types of elementaryreactions.

5.1. Pure n-Octane Cracking Mechanism. 5.1.1. MechanismConstruction. The pyrolysis of n-octane can be described as forthe other n-alkanes by a free-radical mechanism. At low con-version, the elementary reactions include initiation, hydrogentransfer, radical decomposition by β-scission, addition to doublebonds, and termination. To limit the number of reactions andcalculation time, a lumpedmechanismby reaction typehasbeenused. This approach was developed by Bounaceur et al.30,31

Two types of radicals play a part in the pyrolysis mechanism ofsaturated hydrocarbons: radicals that decompose by mono-molecular reactions and radicals that react bybimolecular reac-tions. To represent the homogeneous pyrolysis of an organicsubstance referred to as μH, Goldfinger et al.32 proposed thefollowing nomenclature: (i) a radical that reacts bymonomole-cular reactions is named μ• and (ii) a radical that reacts bybimolecular reactions is named β•.

Using this symbolic representation “β and μ” as well as theelementary reactions presented previously, it is then possibletowrite the primary radicalmechanismdescribing the pyrolysisof a n-alkane (μH).

initiation : μH f free radicals ðtype βÞ

propagation I :μ• f alkeneþβ•

β• þμH f alkane-minus

þμ• ðalkane-minus ¼ βHÞ

terminations :μ• þ μ• f products

β• þ β• f products

β• þ μ• f products

A secondary propagation can be written as

propagation II :alkeneþ μ• f heavy radical•

heavy radical• þμH f alkane-plusþ μ•

The mechanism of n-octane pyrolysis is thus described by 91elementary reactions, including 21molecules and 27 radicals.It is presented in Table A1 in the Appendix. To each reactionis associated a kinetic constant [of kinetic parameters A andEa (in mol, cm3, s, and cal)] as well as, if necessary, an adjust-ment factor (noted ka/ke). The kinetic parameters used arethose proposed by the software EXGAS.33

5.1.2. Validation of the Model. The proposed model ofn-octane pyrolysis is validated by a comparison to experi-mental data (Figure 10). There is a good agreement betweenthe measurements of the remaining reactants after pyrolysisof n-octane and the calculated values. Good agreement forreaction products was also obtained. This suggests that ourmodel takes into account major reactions and can thus be con-sidered as validated. The same results with similar modeling

Figure 6.Partial pressure of n-butane (a pyrolysis product of n-octane)as a function of the pyrolysis time for pure n-octane and variouscompositions of the n-octane/toluene mixture at 350 �C and 700 bar.

(30) Bounaceur, R.; Warth, V.; Glaude, P. A.; Battin-Leclerc, F.;Scacchi, G.; Come, G.-M.; Faravelli, T.; Ranzi, E. Chemical lumping ofmechanisms generated by computer. Application to the modelling ofnormal butane oxidation. J. Chim. Phys. Phys.-Chim. Biol. 1996, 93,1472–1491.

(31) Bounaceur, R.; Warth, V.; Marquaire, P. M.; Scacchi, G.;Domin�e, F.; Dessort, D.; Pradier, B.; Brevart, O. Modeling of hydro-carbons pyrolysis at low temperature. Automatic generation of freeradicals mechanisms. J. Anal. Appl. Pyrolysis 2002, 64 (1), 103–122.

(32) Goldfinger, P.; Letort, M.; Niclause, M. Volume comm�emoratifVictorHenri: Contribution �a l’�etude de la structure mol�eculaire.Desoer,Li�ege 1947-1948, 283.

(33) Warth, V.; Stef, N.; Glaude, P. A.; Battin-Leclerc, F.; Scacchi,G.; Come, G. M. Computer-aided derivation of gas-phase oxidationmechanisms: Application to the modeling of the oxidation of n-butane.Combust. Flame 1998, 114 (1-2), 81–102.

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were obtained on hexadecane pyrolyzed at similar experi-mental conditions.15

5.2. Pure Toluene CrackingMechanism. Toluene pyrolysiswas studied by Lannuzel et al.34 between 350 and 400 �Cunder a pressure of 700 bar, and a detailed kinetic modelconsisting of 30 free-radical reactions was developed todescribe the thermal cracking of toluene at low conversion.The mechanism includes 13 molecules and 8 radicals. Thenomenclature used for the writing of the reactions as well asfor the mechanism is presented in Table A2 in the Appendix.

The main reactions taken into account in our model forhigh-pressure pure toluene pyrolysis are as follows.

5.2.1. Bimolecular Initiations.

These reactions are also called “reverse radical disproportion-ation” (RRD) reactions.11,35,36 The cyclohexadienyl radicals

Figure 7. Chromatogram of the products obtained after the confined pyrolysis of n-C8 pyrolysis at 350 �C and 700 bar for 120 h.

Figure 8. Chromatogram of the pyrolysis products of pure toluene at 450 �C and 700 bar for 2 h.

(34) Lannuzel, F.; Bounaceur, R.; Michels, R.; Scacchi, G.; Mar-quaire, P. M. An extended mechanism including high pressure condi-tions (700 bar) for toluene pyrolysis. J. Anal. Appl. Pyrolysis 2010, 87 (2),236–247.

(35) Benson, S. W. On the reaction between ethylene and cyclopentene,a radical mechanism. Int. J. Chem. Kinet. 1980, 12 (10), 755–760.

(36) Poutsma, M. L. Free-radical thermolysis and hydrogenolysis ofmodel hydrocarbons relevant to processing of coal. Energy Fuels 1990,4 (2), 113–131.

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[with H in ipso (a) or R (b) position] lead by β-scission to theformation of a methyl or hydrogen radical and a benzene ortoluene molecule. Another possibility is the opening of thearomatic ring, which should lead to the formation of C2H2,but this product is not observed in the experiments ofLannuzel et al.,34 and they conclude that this reaction isinsignificant at low temperatures (<450 �C).

5.2.2. Hydrogen Transfer (Metathesis). Two types of hy-drogen-transfer reactions are considered (for example withmethyl radical): (i) Hydrogen abstraction from the benzylicposition leads to the formation of a benzyl radical. (ii) Hydro-gen abstraction from the phenyl position leads to the forma-tion of a phenyl radical.

5.2.3. Ipso Addition (Addition/Elimination).An addition ofa hydrogen radical at the ipso position of a methyl group isfollowed by an elimination reaction, leading to the formationof a methyl radical.

A methyl radical reacts through addition onto an aromaticring, leading to the formation of xylene and a hydrogen radical.

5.2.4. Addition of the Benzyl Radical. The addition ofthe benzyl radical on an aromatic ring and elimination of

a hydrogen atom lead to the formation of methyldiphenyl-methane.

5.2.5. Termination. The combination of benzyl with anotherbenzyl radical leads to the formation of bibenzyl.

5.2.6. Estimation of Rate Constants. The kinetic parametersof the elementary reactions implied in the mechanism are pro-vided in Table A2 in the Appendix (from Lannuzel et al.34).They result from the literature, the National Institute ofStandards and Technology (NIST) database,37 and analogieswhen possible, or they were estimated from semi-empiricalmethods.38

The kinetic parameters of the two bimolecular initiationreactions of toluene were estimated by thermochemicalkinetic methods.34 Calculations give (i) for reaction a, E=71.3 kcal mol-1 and A = 2.5 � 1014 cm3 mol-1 s-1 and(ii) for reaction b, E=68.8 kcal mol-1 and A=2.5 � 1014

cm3 mol-1 s-1.Experimental validation of this mechanism is given in a

previously published paper.34 Figure 11 presents the majorreaction pathways for high-pressure (700 bar) pure toluenepyrolysis at 450 �C.

5.3. Cracking Mechanism of the n-Octane/Toluene Mixture.

In addition to the cracking mechanism for the pure

Figure 9. Chromatogram of the products obtained after pyrolysis at 450 �C and 700 bar for 3 h of the toluene/n-octane mixture (0.9:1).

(37) National Institute of Standards and Technology (NIST). NISTChemical Kinetics Database, NIST Standard Reference Database 17,Version 7.0 (Web Version), Release 1.4.3, Data version 2008.12; NIST:Gaithersburg, MD, 2008; 20899-8320 (http://kinetics.nist.gov/).

(38) Benson, S. W. Thermochemical Kinetics; John Wiley and Sons:New York, 1976.

3824


compounds, major cross-reactions for the n-octane/toluenemixture were added. Hydrogen-transfer, addition, andtermination reactions are systematically written betweenmain species (molecules or radicals). The following reactionshave been taken into account.

(i) H-transfer reactions between toluene and all of theradicals generated by n-octane. For instance:

(ii) H-transfer reactions between n-octane and the mainradicals generated by toluene (benzyl, phenyl, and the hy-drogen radical).

(iii) With regard to the important quantities of alkyl-benzene generated in our experiments at high pressure,addition reactions of the benzyl radical on alkenes wereconsidered

(iv) followed by hydrogen-transfer reactions between reac-tants and alkylbenzene radicals.

(v) Terminations corresponding to the cross-reaction bet-ween the radicals derived from n-C8 and toluene.

The cross-reactions of the n-octane/toluene mixture pyr-olysis consist of 51 elementary reactions, including 36 mole-cules and 15 radicals. They are presented in Table A3 in theAppendix. To each reaction is associated the kinetic para-metersA and E, as well as, if necessary, an adjustment factor(noted F=ka/ke).

5.3.1. Experimental Validation. Figure 12 compares theexperimental results (�) to the results of our model (;) forthe pyrolysis of a n-octane/toluene mixture of 1:0.9 molarratio. There is an overall good agreement for reactantconversion (octane and toluene) as well as reaction pro-ducts (butane for instance). Cross-reaction products arealso well-taken into account by the model (formation ofalkylbenzenes). The model has also been approved by acomparison to other experiments performed in different con-ditions: 330 �C, 100 bar/330 �C, 700 bar/350 �C, 100 bar/350�C, 700 bar.

6. Discussion

6.1. Generic Inhibition Mechanism. In the case of a chainreaction, an inhibitor is a co-reactant that can easilyconvert a radical chain carrier into a less reactive radical,giving new terminations. The rate of the chain reactionthus decreases. Niclause et al.23 proposed a symbolicgeneric mechanism entitled “μH and YH” to describe thepyrolysis of an alkane μH in the presence of compoundscontaining one mobile H atom of the toluene type (notedYH) and yielding a thermally stable and less reactive Y•

radical.Here, the mechanism is based on the hypothesis that the

new initiation reactions from YH are unimportant with re-gards to those of the alkane μH. Considering only the pri-mary radical mechanism, the general principle outlines asfollows (Figure 13). In the presence ofYH, the chain carriers,radicals μ• and β•, can react by metathesis through reactions4μ and 4βwith YH to yield Y•, thermally stable. This radicalcan then either react with μH through reaction 5 or lead tonew termination reactions noted YY, Yβ, and Yμ. Becausereactions 5 and 4μ are reverse reactions, they were groupedtogether.

In the absence of YH, the chain reaction of μH is carriedonly by the radicals μ• andβ• according to propagation I. Thepresence of YH generates a new propagation, noted III,implying the new radical Y• and same stoichiometry as I(alkane-minus is noted βH).

μH ¼ alkene þ alkane-minus

The kinetic effects of YH on the thermal decomposition ofan alkane will then depend upon the relative importance ofthe radicals μ• and β•. (1)When [μ•]. [β•] (low-temperatureand high-pressure conditions), reaction 2 is rate-limiting.The rate of the alkane pyrolysis is then rμH = k2[μ

•]. Theaddition of YH leads to a consumption of the chain carriersμ• and β• and generates Y•, which is likely to react byterminations. The [μ•] radical concentration decreases,and thus, the alkane pyrolysis rate also decreases. In theseconditions, YH acts as an inhibitor on the pyrolysis of μHthrough new termination reactions YY and Yμ. (2) When[β•]. [μ•] (high-temperature and low-pressure conditions),reaction 3 is rate-limiting. The rate of octane pyrolysis isthen equal to rμH = k3[β

•][μH] þ k4β[β•][YH]. The co-

reactant YH has two effects on the alkane pyrolysis: (i) anaccelerating effect because of the new propagation III,leading to the same products of reaction as propagation I,and (ii) an inhibitive effect by consuming the chain carriersμ• and β• (reactions 4μ and 4β), to yield a less reactiveradical Y•, which leads to new termination reactionsYβ andYY. The [β•] radical concentration decreases, and therefore,

3825


the octane pyrolysis rate also decreases. The result of both of

these kinetic effects of YH on μH depends upon P and T

conditions and the ability of Y• to react. When Y• is not veryreactive, its concentration is high and leads to important new

terminations. The global kinetic effect ofYH is an inhibition.

When Y• is more reactive, its concentration is very low and

the new terminations are unimportant. The co-reactant YHmay globally accelerate the decomposition of μH through

propagation III.6.2. Application of the Generic Inhibition Mechanism to

Toluene. Because of its structure, toluene is a YH com-pound type (hydrogen donor). Because of the presence of

the aromatic ring, hydrogen-transfer reactions may occur

between alkyl radicals and toluene, leading to the benzylradical, stabilized by resonance. Its influence on alkanecracking follows the “μH and YH”mechanism (Y• representsthe benzyl radical). (i) At low-pressure and high-temperatureexperiments, [β•] . [μ•]. Because the benzyl radical is stabi-lized by resonance, it has low reactivity and the global kineticeffect of toluene is an inhibition. Hence, inhibition of thecracking of alkanes is observed at high-temperature andlow-pressure experiments. (ii) At high-pressure and low-temperature conditions, [μ•] . [β•] and toluene should actas an inhibitor on the pyrolysis of n-octane. However, thisis not the case in our experiments (Figures 5 and 6). A closeexamination of the chromatograms of the reaction products

Figure 10.Comparison of themeasuredmolar fraction of the remaining reactants and selected reaction products (b) tomodeled values (;) forthe pyrolysis of pure n-octane at 330 and 350 �C at 700 bar as a function of time.

3826


(Figure 9) allows us to provide evidence of a major class of

compounds not described by the published “μH and YH”

mechanism for toluene. These compounds are all alkylben-

zenes (from propylbenzene to octylbenzene), resulting from

the addition of the benzyl radical on alkenes (from ethylene

to heptene).In the mechanism “μH and YH” described above, the

inhibitive effect resulted from the consumption of chain

carriers μ• and β• by the reaction with toluene to give aless reactive and thermally stable radical Y•, leading to newtermination reactions. If, now, the addition of Y• on alkenesis taken into account, part of the radicals Y• are transformedinto more reactive radicals R• of type β• (chain-carrier radical),leading to a decrease in the inhibition. The generic mechanism“μH and YH”, taking into account these addition reactions,must then be completed the following way (by reminding the

Figure 11. Main reaction pathways for pyrolysis of pure toluene at 700 bar and 450 �C. Percentages indicated refer to the rate ratio of thereaction processes to toluene consumption.

Figure 12. Validation of the n-octane-toluene kinetic model by a comparison of the experimental results (�) to the results of our model (;).Data shown account for the reactants (n-octane and toluene), themajor products derived from octane (n-butane), and themajor cross-reactionproducts (alkylbenzenes) at 450 �C and 700 bar for an initial n-octane/toluene mixture (1:0.9 molar ratio).

3827


secondary chain propagation II described in the pure octanepyrolysis mechanism):

A new propagation appears, noted IV, implying the newradical R• and giving the following stoichiometry:

YHþ alkene ¼ RH

This typical mechanism “μH and YH improved” can beschematized as in Figure 14.

Using the mechanism, the evolution of the IF at 350 �Cand 700 bar and at 500 �C and 0.03 bar as a function of con-version is calculated in Figure 15 for a n-C8/toluenemixture

(9:1 molar ratio). (i) At high temperature and low pressure(500 �C and 0.03 bar), the radical chain carrier β• isdominant ([β•] . [μ•]). At low conversion, inhibition isobserved: IF > 5, and the reaction mechanism works asclassical “μH and YH”. When the conversion increases, theproduced alkenes increase, consequently leading to moreaddition reactions. Thus, the benzyl radical concentration(Y•) decreases as well as the IF. (ii) At low temperature andhigh pressure (350 �C and 700 bar), the radical chain carrierμ• is dominant ([μ•] . [β•]) and toluene should act as aninhibitor on the pyrolysis of n-octane. However, the high-pressure conditions favor the radical addition reactions. Atvery low conversion (X<10-4), inhibition is observed (IF=2.5) because the alkene concentrations are too low to quenchmost of benzyl radicals. When conversion increases, theproduced alkenes increase while they react with the benzylradical, leading to a significant decrease of inhibition. Atconversion close to 1%, IF is about 1.2 and tends toward 1with further progress.

Figure 13. Scheme summarizing the generic action of an in-hibitor YH on the pyrolysis of an alkane μH (after Niclauseet al.23).

Figure 14. Diagram representing the action of an inhibitor YH onthe pyrolysis of an alkane μH and taking into account the additionof Y• on alkenes.

Figure 15. Evolution of the calculated IF as a function of n-octaneconversion at 350 �Cand 700 bar and at 500 �Cand 0.03 bar for a 9:1n-C8/toluene molar mixture.

3828


7. Conclusion

At very low pressure (a few millibars), toluene inhibitsthe pyrolysis of alkanes regardless of the temperature (350-500 �C). Its actionmechanismof type“μHandYH”was clearlyidentified. The objective of this work aimed at checking if thiscompound kept the same behavior at high pressure (severalhundreds of bars). Our experiments, carried out between 350and 450 �C for pressures of 100 and 700 bar, did not show asignificant inhibition under these conditions. The analysis ofthe products of pyrolysis of n-C8/toluene mixtures allowed ustodevelopamechanismandelucidate the difference in toluenereactivity between the high and low pressures. Thus, theabsence of inhibition at 350 �C at high pressures is explainedby an addition reaction of the benzyl radicals on alkenes,negligible at low pressures. This new reaction implies that theinhibiting behavior of toluene evolves with temperature,pressure, and reaction progress. Inhibition will decrease withreaction progress and a pressure increase. Our study revealsthat the inhibition effect of toluene on alkane pyrolysis canvary drastically as a function of reaction conditions but can bepredicted by our kinetic model.

A further study will explore, by simulation, the influence oftoluene on alkane pyrolysis in geological conditions, i.e., atlow temperatures (200 �C)andhighpressures (100-1000bar).These results should enable us to predict the influence ofmethyl aromatics on the thermal stability of oils in geologicalreservoirs.

Acknowledgment. This work was supported by TOTALExploration and Production (Pau, France).

Appendix

Table A1. n-Octane Cracking Mechanisma

reactions A E

Primary Mechanism

Initiations1 n-C8 f C4H9• þ C4H9• 1.10� 1017 834082 n-C8 f C3H7• þ C5H11• 1.10� 1017 838373 n-C8 f C2H5• þ C6H13• 1.10� 1017 837964 n-C8 f CH3• þ C7H15• 1.10� 1017 85674

Decompositions5 μ8• f CH3• þ C7H14-A 2.00� 1013 310006 μ8• f C2H5• þ C6H12-A 2.00� 1013 287007 μ8• f C3H7• þ C5H10-A 2.00� 1013 287008 μ8• f C4H9• þ C4H8-A 2.00� 1013 287009 μ8• f C5H11• þ C3H6-A 2.00� 1013 2870010 μ8• f C6H13• þ C2H4-A 2.00� 1013 2870011 C6H13• f CH3• þ C5H10-A 2.00� 1013 3100012 C6H13• f C2H5• þ C4H8-A 2.00 � 1013 2870013 C6H13• f C3H7• þ C3H6-A 2.00� 1013 2870014 C6H13• f C4H9• þ C2H4-A 2.00� 1013 2870015 C5H11• f CH3• þ C4H8-A 2.00� 1013 3100016 C5H11• f C2H5• þ C3H6-A 2.00� 1013 2870017 C5H11• f C3H7• þ C2H4-A 2.00� 1013 2870018 C4H9• f CH3• þ C3H6-A 2.00� 1013 3100019 C4H9• f C2H5• þ C2H4-A 2.00� 1013 2870020 C3H7• f CH3• þ C2H4-A 2.00� 1013 31000

Metathesis

21 n-C8 þ CH3• f μ8• þ CH4 2.00� 1011 960022 n-C8 þ C2H5• f μ8• þ C2H6 2.00� 1011 1120023 n-C8 þ C3H7• f μ8• þ C3H8 2.00� 1011 1120024 n-C8 þ C4H9• f μ8• þ C4H10 2.00� 1011 1120025 n-C8 þ C5H11• f μ8• þ C5H12 2.00� 1011 1120026 n-C8 þ C6H13• f μ8• þ C6H14 2.00� 1011 11200

Table A1. Continued

reactions A E

Recombinations

27 CH3• þ CH3• f C2H6 3.00� 1013 028 C2H5• þ C2H5• f C4H10 1.00� 1013 029 C3H7• þ C3H7• f C6H14 5.00� 1011 030 C4H9• þ C4H9• f n-C8 5.00� 1011 031 C5H11• þ C5H11• f C10H22 5.00� 1011 032 C6H13• þ C6H13• f C12H26 5.00� 1011 033 μ8• þ μ8• f C16H34 5.00� 1011 034 CH3• þ C2H5• f C3H8 1.00� 1013 035 CH3• þ C3H7• f C4H10 5.00� 1011 036 CH3• þ C4H9• f C5H12 5.00� 1011 037 CH3• þ C5H11• f C6H14 5.00� 1011 038 CH3• þ C6H13• f C7H16 5.00� 1011 039 CH3• þ μ8• f C9H20 5.00� 1011 040 C2H5• þ C3H7• f C5H12 5.00� 1011 041 C2H5• þ C4H9• f C6H14 5.00� 1011 042 C2H5• þ C5H11• f C7H16 5.00� 1011 043 C2H5• þ C6H13• f n-C8 5.00� 1011 044 C2H5• þ μ8• f C10H22 5.00� 1011 045 C3H7• þ C4H9• f C7H16 5.00� 1011 046 C3H7• þ C5H11• f n-C8 5.00� 1011 047 C3H7• þ C6H13• f C9H20 5.00� 1011 048 C3H7• þ μ8• f C11H24 5.00� 1011 049 C4H9• þ C5H11• f C9H20 5.00� 1011 050 C4H9• þ C6H13• f C10H22 5.00� 1011 051 C4H9• þ μ8• f C12H26 5.00� 1011 052 C5H11• þ C6H13• f C11H24 5.00� 1011 053 C5H11• þ μ8• f C13H28 5.00� 1011 054 C6H13• þ μ8• f C14H30 5.00� 1011 0

Secondary Mechanism

Additions

55 μ8• þ C2H4-A f C10H21• 4.00� 1011 800056 μ8• þ C3H6-A f C11H23• 4.00� 1011 800057 μ8• þ C4H8-A f C12H25• 4.00� 1011 800058 μ8• þ C5H10-A f C13H27• 4.00� 1011 800059 μ8• þ C6H12-A f C14H29• 4.00� 1011 800060 μ8• þ C7H14-A f C15H31• 4.00� 1011 8000

Decompositions61 C10H21• f C3H7• þ C7H14-A 4.00� 1013 2870062 C10H21• f C4H9• þ C6H12-A 4.00� 1013 2870063 C10H21• f C5H11• þ C5H10-A 4.00� 1013 2870064 C10H21• f CH3• þ C9H18-A 4.00� 1013 3100065 C11H23• f C4H9• þ C7H14-A 4.00� 1013 2870066 C11H23• f C3H7• þ C8H16-A 4.00� 1013 2870067 C11H23• f C5H11• þ C6H12-A 4.00� 1013 2870068 C11H23• f CH3• þ C10H20-A 4.00� 1013 3100069 C12H25• f C4H9• þ C8H16-A 3.00� 1013 2870070 C12H25• f C5H11• þ C7H14-A 3.00� 1013 2870071 C12H25• f C3H7• þ C9H18-A 3.00� 1013 2870072 C12H25• f CH3• þ C11H22-A 3.00� 1013 3100073 C13H27• f C5H11• þ C8H16-A 3.00� 1013 2870074 C13H27• f C4H9• þ C9H18-A 3.00� 1013 2870075 C13H27• f C3H7• þ C10H20-A 3.00� 1013 2870076 C13H27• f CH3• þ C12H24-A 3.00� 1013 3100077 C14H29• f C5H11• þ C9H18-A 3.00� 1013 2870078 C14H29• f C6H13• þ C8H16-A 3.00� 1013 2870079 C14H29• f C4H9• þ C10H20-A 3.00� 1013 2870080 C14H29• f C3H7• þ C11H22-A 3.00� 1013 2870081 C14H29• f CH3• þ C13H26-A 3.00� 1013 3100082 C15H31• f C5H11• þ C10H20-A 3.00� 1013 2870083 C15H31• f C4H9• þ C11H22-A 3.00� 1013 2870084 C15H31• f C3H7• þ C12H24-A 3.00� 1013 2870085 C15H31• f CH3• þ C14H28-A 3.00� 1013 31000

Metathesis86 n-C8 þ C10H21• f μ8• þ C10H22 4.00� 1011 1220087 n-C8 þ C11H23• f μ8• þ C11H24 4.00� 1011 1220088 n-C8 þ C12H25• f μ8• þ C12H26 4.00� 1011 1220089 n-C8 þ C13H27• f μ8• þ C13H28 4.00� 1011 1220090 n-C8 þ C14H29• f μ8• þ C14H30 4.00� 1011 1220091 n-C8 þ C15H31• f μ8• þ C15H32 4.00� 1011 12200

aUnits: mol, cm3, s, and cal.

3829


Table A2. Toluene Cracking Mechanisma

reactions A n E

Unimolecular Initiation1 toluene f benzyl• þ H• 3.10� 1015 0 892002 benzyl• þ H• f toluene 2.59� 1014 0 03 toluene f C6H5• þ CH3• 1.00� 1017 0 970004 C6H5• þ CH3• f toluene 1.39� 1013 0 0

Bimolecular Initiation5 toluene þ toluene f benzyl• þ C6H6CH3a• 2.50� 1014 0 713006 toluene þ toluene f benzyl• þ C6H6CH3b• 2.50� 1014 0 68800

Ipso Additions7 toluene þ H• f C6H6 þ CH3• 1.20� 1014 0 81008 toluene þ CH3• f xylene þ H• 5.00� 1012 0 159409 xylene þ CH3• f trimethylbenzene þ H• 3.00� 1012 0 15940

Metathesis on a Benzylic H Atom10 toluene þ H• f benzyl• þ H2 1.20� 1014 0 840011 toluene þ CH3• f benzy•l þ CH4 4.00� 1011 0 1110012 toluene þ C3H5V• f benzyl• þ C3H6V 4.00� 1012 0 800013 toluene þ C6H5• f benzyl• þ C6H6 7.90� 1013 0 1200014 toluene þ C6H4CH3• f benzyl• þ toluene 7.90� 1013 0 12000

Metathesis on a Phenylic H Atom15 toluene þ H• f C6H4CH3• þ H2 6.00� 108 1 1680016 toluene þ CH3• f C6H4CH3• þ CH4 2.00� 1012 0 15000

C6H6CH3• Decomposition17 C6H6CH3a• f 2C2H2T þ C3H5V• 2.00 � 1013 0 2170018 C6H6CH3b• f 3C2H2T þ CH3• 2.00� 1013 0 2170019 C6H6CH3a• f 2C2H2T þ C3H4 þ H• 2.00� 1013 0 2170020 C6H6CH3a• f toluene þ H• 2.00� 1013 0 2870021 C6H6CH3b• f C6H6 þ CH3• 2.00� 1013 0 28700

Benzyl Additions on Aromatic Ring22 benzyl• þ C6H6 f benzylphenyl þ H• 2.00� 1012 0 2300023 benzyl• þ toluene f benzylphenyl þ H• 2.00� 1012 0 2300024 benzyl• þ xylenef benzylphenyl þ H• 2.00� 1012 0 23000

Terminations25 2 benzyl• f bibenzyl 2.50� 1011 0.4 026 benzyl• þ CH3• f etC6H5 5.00� 1012 0 027 benzyl• þ C3H5V• f benzC3H5V 5.00� 1012 0 028 C6H4CH3• þ H• f toluene 1.00� 1014 0 029 C6H4CH3• þ CH3• f xylene 1.00� 1013 0 030 CH3• þ CH3• f C2H6 3.00� 1013 0 0

a cf. ref 34.

Table A3. Cross-reactions of the n-Octane/Toluene Mixture Pyrolysis

reactions A n E F

Metathesis1 toluene þ μ8• f benzyl• þ n-C8 0.32 3.3 85592 n-C8 þ benzyl• f μ8• þ toluene 120 3.3 18170 �3.53 toluene þ C2H5• f benzyl• þ C2H6 1.20� 1011 0 134004 toluene þ C3H7• f benzyl• þ C3H8 1.20� 1011 0 134005 toluene þ C4H9• f benzyl• þ C4H10 1.20� 1011 0 134006 toluene þ C5H11• f benzyl• þ C5H12 1.20� 1011 0 134007 toluene þ C6H13• f benzyl• þ C6H14 1.20� 1011 0 134008 toluene þ C10H21• f benzyl• þ C10H22 1.20� 1011 0 134009 toluene þ C10H21• f benzyl• þ C10H22 1.20� 1011 0 1340010 toluene þ C12H25• f benzyl• þ C12H26 1.20� 1011 0 1340011 toluene þ C13H27• f benzyl• þ C13H28 1.20� 1011 0 1340012 toluene þ C14H29• f benzyl• þ C14H30 1.20� 1011 0 1340013 toluene þ C15H31• f benzyl• þ C15H32 1.20� 1011 0 1340014 benzyl• þ C2H6 f toluene þ C2H5• 120 3.3 1817015 benzyl• þ C3H8 f toluene þ C3H7• 120 3.3 1817016 benzyl• þ C4H10 f toluene þ C4H9• 120 3.3 1817017 benzyl• þ C5H12 f toluene þ C5H11• 120 3.3 1817018 benzyl• þ C6H14 f toluene þ C6H13• 120 3.3 1817019 benzyl• þ C7H16 f toluene þ C7H15• 120 3.3 1817020 benzyl• þ C10H22 f toluene þ C10H21• 120 3.3 1817021 benzyl• þ C11H24 f toluene þ C11H23• 120 3.3 1817022 benzyl• þ C12H26 f toluene þ C12H25• 120 3.3 18170

3830


Table A3. Continued

reactions A n E F

23 benzyl• þ C13H28 f toluene þ C13H27• 120 3.3 1817024 benzyl• þ C14H30 f toluene þ C14H29• 120 3.3 1817025 benzyl• þ C15H32 f toluene þ C15H31• 120 3.3 18170

Reactions on Alkenes

25 C2H4 þ benzyl• f benzylcenyl• 2.00� 1011 0 600026 C3H6 þ benzyl• f benzylcenyl• 2.00� 1011 0 600027 C4H8 þ benzyl• f benzylcenyl• 2.00� 1011 0 600028 C5H10 þ benzyl• f benzylcenyl• 2.00� 1011 0 600029 C6H12 þ benzyl• f benzylcenyl• 2.00� 1011 0 600030 C7H14 þ benzyl• f benzylcenyl• 2.00� 1011 0 600031 C8H16 þ benzyl• f benzylcenyl• 2.00� 1011 0 600032 C9H18 þ benzyl• f benzylcenyl• 2.00� 1011 0 600033 C10H20 þ benzyl• f benzylcenyl• 2.00� 1011 0 600034 C11H22 þ benzyl• f benzylcenyl• 2.00� 1011 0 600035 C12H24 þ benzyl• f benzylcenyl• 2.00� 1011 0 600036 C13H26 þ benzyl• f benzylcenyl• 2.00� 1011 0 600037 C14H28 þ benzyl• f benzylcenyl• 2.00� 1011 0 600038 C15H30 þ benzyl• f benzylcenyl• 2.00� 1011 0 600039 C16H32 þ benzyl• f benzylcenyl• 2.00� 1011 0 600040 benzylcenyl• þ n-C8 f benzylcene þ μ8• 3.20� 1012 0 1400041 benzylcenyl• þ toluene f benzylcene þ benzyl• 0.32 3.3 855942 n-C8 þ H• f μ8• þ H2 1.60� 1012 0 1117543 n-C8 þ C6H5• f μ8• þ C6H6 2.65� 1011 0 3880

Terminations

44 benzyl• þ μ8• f nonylbenzene 1.60� 1011 0 045 benzyl• þ C7H15• f octylbenzene 1.60� 1011 0 046 benzyl• þ C6H13• f heptylbenzene 1.60� 1011 0 047 benzyl• þ C5H11• f hexylbenzene 1.60� 1011 0 048 benzyl• þ C4H9• f pentylbenzene 1.60� 1011 0 049 benzyl• þ C3H7• f butylbenzene 1.60� 1011 0 050 benzyl• þ C2H5• f proylbenzene 1.60� 1011 0 051 benzyl• þ CH3• f ethylbenzene 1.60� 1011 0 0

Documents

Reassessment of the Kinetic Influence of Toluene on n -Alkane Pyrolysis