mechanistic modeling of the thermal cracking of tetralin

Mechanistic Modeling of the Thermal Cracking of Tetralin

Roda Bounaceur, Gerard Scacchi, and Paul-Marie Marquaire*

Departement de Chimie Physique des Reactions (UMR n°7630 CNRS, INPL-ENSIC) 1, rue Grandville,BP 451, 54001 Nancy Cedex, France

Florent Domine*

Carbochem, 12 chemin de Maupertuis, 38240 Meylan, France

A detailed kinetic model consisting of 132 free-radical reactions has been developed to describethe thermal cracking of tetralin. The model was tested against available experimental data fortetralin pyrolysis in the temperature range 350-500 °C. The importance of the knowledge ofthe impurity levels in the tetralin used for any experiment has been shown. The formation ofthe main products, namely, 1-methylindane, naphthalene, and n-butylbenzene, is correctlydescribed. The production of 1-methylindane is due to the contraction of the saturated ring.Naphthalene is formed by dehydrogenation reactions. The production of butylbenzene is due tothe ipso addition of a hydrogen atom to tetralin. When the temperature increases, the formationof 1-methylindane decreases, whereas those of n-butylbenzene and naphthalene increase.

Introduction

Tetralin (1,2,3,4-tetrahydronaphthalene) has longbeen recognized as an effective hydrogen donor.1 It is arepresentative of a series of hydroaromatic hydrocar-bons used in the coal liquefaction processes.2-4 Tetralinis an efficient hydrogen donor because its hydrogenatoms, in particular those in the R position of thesaturated ring, can be readily abstracted by radicalsgenerated during thermal processing. H-donor additivessuch as tetralin have been shown to effectively reduceor eliminate the formation of solids in the pyrolysis ofactual jet fuels at representative aircraft fuel systemconditions and then to improve their thermal stability.5,6

Preliminary attempts to explain the formation ofdecomposition products involve free-radical reactions,7but no quantitative tests of the proposed mechanismhave been performed, probably because of the unavail-ability of rate constant data.

A brief review of the thermal transformation oftetralin gives the following results.

Hooper et al.8 heated tetralin for various periods from2 to 6 h at temperatures between 300 and 450 °C. Themajor product was 1-methylindane. Other products, inorder of decreasing selectivity, were naphthalene, bu-tylbenzene, ethylbenzene, indane or indene, and tolu-ene. Yen et al.9 proposed disproportionation reactionsfor the formation of naphthalene, but according toHooper, the identification of gaseous hydrogen in thereaction products provides evidence that the naphtha-lene found was formed by dehydrogenation rather thana disproportionation process. The author explains theformation of ethylbenzene, propylbenzene, and tolueneas products from the side-chain cracking of butylben-zene, which is itself formed from R-ring opening of thetetralin. Toluene has also been reported as a productfrom ring opening of 1-methylindane and indane by ademethylation of 1-methylindane.

In a review, Poutsma7 gave the following majorclasses of products from thermal cracking of tetralin:(1) ring contraction to form 1-methylindane, indane, andindene; (2) dehydrogenation to form 1,2-dihydronaph-thalene and naphthalene; (3) ring-opening hydrogenoly-sis to form butylbenzene; and (4) loss of two carbons andcracking to form benzocyclobutene, styrene, and alkyl-benzene. For liquid and dense supercritical tetralinaround 400 °C, these reactions fall in the order ringcontraction > dehydrogenation > ring opening . C2loss.

Grigor′eva et al.10-12 studied the pyrolysis of tetralinbetween 450 and 510 °C and at a total pressure ofaround 14 MPa (tetralin pressurized by H2). The mainproducts were 1-methylindane, naphthalene, and n-butylbenzene, whereas minor products were ethylben-zene, toluene, and o-xylene. A kinetic model of thermol-ysis was given by Grigor′eva that correctly describesmain pyrolysis products (1-methylindane, naphthalene,and n-butylbenzene) without considering secondarytransformations. According to an array of data for 30experiments, rate constants were computed by solvinga system of differential equations. Moreover, an experi-mental value for the activation energy of 59 kcal/molin the temperature range of 350-550 °C was found.

A number of thermal cracking experiments wereperformed by Khorasheh and Gray13 using neat tetralinat typical reaction conditions (13.9 MPa, 430-450 °C, t≈ 1 h). The major products found were the same asthose found by the other authors. Minor productsincluded trace quantities of some C10 compounds, suchas methyl phenyl propene, resulting from the decom-position of tetralyl radicals, and a mixture of C20compounds, possibly resulting from combinations oftetralyl radicals or the addition of tetralyl radicals to1,2 dihydronaphthalene. Khorasheh and Gray noticedthat Frantz et al.14 identified C20 compounds producedfrom the thermal decomposition of 1,2-dihydronaphtha-lene. According to the authors, the formation of thesecompounds is due to the addition of tetralyl or dihy-dronaphthyl radicals to 1,2-dihydronaphthalene. Kho-

* Corresponding authors. E-mails: [email protected], [email protected].

4152 Ind. Eng. Chem. Res. 2000, 39, 4152-4165

10.1021/ie000276f CCC: $19.00 © 2000 American Chemical SocietyPublished on Web 10/03/2000

rasheh proposed an alternative mechanism for thehydrogenolysis of tetralin via a radical hydrogen trans-fer (RHT) mechanism, which consists of reactions inwhich a radical donates a â-hydrogen to an unsaturatedacceptor. Originally, this mechanism was proposed byMcMillen et al.1,15,16 to be responsible for bond scissionduring coal pyrolysis. RHT has long been suggested asa likely mechanism for cleavage of aryl-alkyl bonds inthe pyrolysis of polyaromatic alkylarenes.17-20

Despite the numerous studies on the thermal trans-formation of tetralin, mechanisms of its decompositionare still unclear. The purpose of the present study is tocontribute to the elucidation of the mechanism of thetransformation of pure tetralin. Our objective is to useall of the previous results to investigate all probablereaction pathways and then construct a radical reactionmechanism with kinetics data in Arrhenius form toexplain the formation of primary and secondary prod-ucts.

Model ConstructionOn the basis of free-radical reactions, a kinetic model

for the thermal transformation of tetralin has beenconstructed. A systematic approach was used to buildthe reaction mechanism for formation of primary prod-ucts. We have decided to include some secondary reac-tions in which molecules formed in the primary mech-anism react to form other molecules and new radicals.Thus, we obtain a detailed primary mechanism and apartial secondary mechanism. We will detail below eachtype of reaction considered.

Primary Mechanism. This primary mechanismincludes all of the different elementary free-radicalreactions: initiation, RHT, H-transfer, isomerization,ring contraction, decomposition, addition, and termina-tion.

Figure 1 illustrates some examples of typical reactionsused in the model.

Initiation Reactions. Initiation reactions include mono-molecular homolysis. Thermodynamic calculations (seeAppendix 1) lead to the estimation of bond strengthsfor the various linkages in tetralin. The result is shownin Figure 2.

For tetralin, the most important homolysis reactionsare the scissions of the â C-C bond on the saturatedcycle, leading to the formation of a biradical (reaction1), and of the weakest C-H bond, giving the 1-tetralylradical (reaction 2).

Radical Hydrogen-Transfer Reactions (Reaction 3).The importance of RHT reactions has been the subjectof some controversy, because these reactions transfer ahydrogen atom from a radical (thus forming a doublebond) to a closed-shell molecule. Franz et al.,21 with thesupport of quantum calculations, claimed that thesereactions should be unimportant. Savage,22 however,reviewed the RHT controversy and explained that thepyrolysis of 1-dodecylpyrene could not be modeledwithout RHT reactions. Although a good fit betweenexperimental and model cannot be taken as an indis-putable proof of validity of a model, in view of the workof Savage and of the success encountered by Malhotraand McMillen23 in modeling the pyrolysis of hydroaro-matics using RHT reactions, we have taken the optionof including such reactions in the present model.

H-Transfer Reactions (Reaction 4). Reactions in whichradicals abstract hydrogen from tetralin were included.The formation of 1- and 2-tetralyl was included in mostcases.

Isomerization Reactions (Reaction 5). The most im-portant isomerization is the bimolecular reaction, whichtransforms the radical 1-tetralyl to 2-tetralyl.7

Ring Contraction Reactions (Reaction 6). This reac-tion, studied by Frantz and Camaioni,24 is a radicalisomerization with a neophilic regrouping that producesthe 1-methylindyl radical.

Decomposition Reactions by â-Scission. We take intoaccount C-C (reaction 7) and C-H (reaction 8) decom-positions of all radicals formed in the primary mecha-nism.

Addition Reactions. Different types of additions havebeen taken into account: intramolecular addition (reac-tion 9), leading to 1-methylindyl, or ipso addition(reaction 10) of a hydrogen atom followed by R-scissionof the aryl-alkyl bond, producing n-butylbenzyl radi-cal1.

Termination by Disproportionation or RecombinationReactions. Reactions between certain radicals (mostly1-tetralyl and 2-tetralyl radicals) formed in the primarymechanism were included in the model (reactions 11and 12).

Secondary Mechanism. This secondary mechanismincludes the same elementary free-radical reaction typesas above, but now it involves molecules formed in theprimary mechanism. We have decided to include somereactions involving 1-methylindane, 1,2-dihydronaph-thalene, and n-butylbenzene to explain the formationof products such as naphthalene or indane.

Figure 3 illustrates some examples of typical reactionsused in the model.

Initiation Reactions. Initiation reactions include bi-molecular reverse radical disproportionation (RRD)reactions. Small amounts of impurities (such as naph-thalene and 1,2-dihydronaphthalene) likely act as radi-cal precursors, so including bimolecular RRD initiationsis necessary. The RRD reactions used were thoseinvolving tetralin, naphthalene, and 1,2-dihydronaph-thalene, which are products of tetralin pyrolysis (reac-tions 13 and 14).

Radical Hydrogen Transfer Reactions (Reaction 15).See primary mechanism.

H-Transfer Reactions (Reaction 16). See primarymechanism.

Decomposition Reactions by â-Scission (Reactions 17and 18). See primary mechanism.

Addition Reactions. We include bimolecular additions(reaction 19) leading to alkyltetralin and ipso addition(reaction 20) also.

Disproportionation Reactions (Reaction 21). Refer toprimary mechanism. Note that the disproportionationreaction will generate 1,2-dihydronaphthalene, whichis involved in RRD reactions.

Thus, we obtain a detailed primary mechanism, whichalso includes some secondary reactions and whichcomprises 132 free-radical reactions. This mechanismis reported in Appendix 2.

The products whose formations are predicted by ourmechanism are listed in Table 1.

Estimation of Rate Constants

The parameters of most of the thermal reactions inour mechanism have not been measured directly, sodifferent methods have been employed to estimate them.For some reactions, the compilation of Allara andShaw25 or the NIST database26 was used. For otherreactions, the parameters were estimated from analo-

Ind. Eng. Chem. Res., Vol. 39, No. 11, 2000 4153

gous reactions, with changes taking into account ther-mochemistry. We also used the software KINGAS,27

which is a computer program for the estimation of rateparameters (both the A factor and the activation energyE) by the methods of Benson.28 Nevertheless, for mostreactions the methods described above were inefficient,so the reaction-family concept was used to estimate therate constant for several reactions. This is based on theuse of a linear free energy relationship29,30 (LFER).Malhotra and McMillen23 and Walter and Klein31 havedemonstrated the validity of the LFER concept usingan Evans-Polanyi32 relationship for correlating rate

Figure 1. Examples of typical reactions used in the primary mechanism to model the thermal cracking of tetralin.

Figure 2. Estimated bond dissociation energies (kcal/mol) intetralin.

4154 Ind. Eng. Chem. Res., Vol. 39, No. 11, 2000

constants to heats of reaction for free-radical reactionfamilies. For each reaction, the Evans-Polanyi relation-ship links the activation energy Ef of a forward reactionto its reaction enthalpy ∆rH°. In the case of an endo-thermic reaction, this relationship can be written

where Eo is the activation energy for the thermoneutral

case and R is the Evans-Polanyi parameter. For thereverse reaction, we can write

Thus, estimation of the rate parameter with the Evans-Polanyi relationship requires the knowledge of reactionthermochemistry (see Thermochemical Properties be-low).

Figure 3. Examples of typical reactions used in the secondary mechanism.

Table 1. Species formed in the mechanism

1-methylindane indene indane benzocyclobutanenaphthalene 1,2 dihydronaphthalene ethyltetralin propyltetralinn-butylbenzene propylbenzene ethylbenzene tolueneo-propyltoluene o-propenyltoluene o-ethylstyrene o-xylenephenylbutene propenylbenzene styrene C20 coumpoundsCH4, C2H6, C3H8 C2H4, C3H6 H2

Ef ) Eo + (1 - R)∆rH° (E1)

Er ) Eo - R∆rH° (E2)


In Table 2, we summarize the rate parameters of eachreaction family.23

Thermochemical Properties

The heats of formation ∆fH° and entropies S° of thespecies used (both molecules and radicals) are listed inAppendix 3. Depending on the available data and theproblem to be solved, different methods were used toestimate thermodynamic data, such as reviews, extrapo-lation from analogous compounds, bond dissociationenergies (BDEs), group additivities,28 or the softwareTHERGAS,36 which is a computer program for theevaluation of thermochemical data for molecules andfree radicals using the methods of Benson28 and Yone-da.37 Knowledge of the heats of formation ∆fH° andentropies S° is necessary for the calculation of thekinetic data using the Evans-Polanyi32 relationship andfor the estimation of the kinetic data for the reversereactions using the following relationships (e.g., Ben-son28):

whereE1 ) activation energy of the forward reaction in kcal/

molE-1 ) activation energy of the reverse reaction in kcal/

molA1 ) A factor for the forward reaction in L mol sA-1 ) A factor for the reverse reaction in L mol s∆rH° ) enthalpy of reaction in kcal/mol∆rS° ) entropy of reaction in cal mol-1 K-1

∆n ) variation of the mole numberR ) gas constantR1 ) 0.082 L atm mol-1 K-1

C° ) 1 mol L-1

P°)1 atmT ) temperature in K

Experimental Validation

A first test of the mechanism was performed bycomparing model output with the experimental data ofKhorasheh and Gray13 at 13.9 MPa, 430-450 °C, andresidence times around 1h; the authors give only themolar ratio of product i (Xi) relative to that of n-butylbenzene (Xbut). Without more information, simula-tions were performed at 13.9 MPa, 440 °C, a residence

time of 70 min, and an initial reactant mixture com-posed of 99 mol % of tetralin and 1 mol % of naphtha-lene, using the software CHEMKIN II.38 In Table 3, wecompare the experimental and simulated values of theratio Xi/Xbut (second and third columns), after minor ratecoefficient adjustments (see Appendix 2) to improve thefit between the model and experimental results.

We can conclude that we obtain a good agreementbetween the experimental and simulated values for allof the compounds except for naphthalene. The reasonis probably due to the impurity level in the reactantused. Indeed, a chromatographic analysis of the tetralinused by Khorasheh and Gray13 indicated the presenceof naphthalene, cis- and trans-decaline, and an uniden-tified compound as major impurities. These impuritiesaccounted for approximately 1 wt % of the feed. In ourcase, we considered that the impurity was only naph-thalene. The result of a simulation at 13.9 MPa, 440°C, a residence time of 70 min, and using an initialreactant composed of pure tetralin is shown in Table 3.It is clear that knowledge of the impurity level in thereactant is very important because, with no initialnaphthalene, the total amount of tetralin, after 70 minof residence time, is equal to 0.65 (compared to 6.3). Wewill later show the influence of impurities on tetralinconsumption.

A comparison of the model output with the experi-mental data of Yu and Eser39 at 450 °C and 40 barrepresented another test of our mechanism. Theseauthors used an initial reactant mixture composed of98.7 wt % of tetralin and 1.3 wt % of component suchas naphthalene, 1,2-dihydronaphthalene, Decalin, 1-methylindan, toluene, benzene, 1-tetralone, 1-tetralol,and an unidentified compound that eluted between cis-decalin and 1-methylindane. For this comparison, an

Table 2. Rate Parameters for Reaction Types in Figures 1 and 3

reaction type A factora (L mol s) activation energy E (kcal/mol) comments

RRD 109.5(RPD/8) 9 + 0.82∆rH° If ∆rH° g 50 w E ) ∆rH°RD 109.4(RPD/4) 9 - 0.18∆rH° If ∆rH° e 50 w E ) 0RHT 108.1(RPD/2) 16.5 + 0.65∆rH° endothermic

16.5 - 0.35(-∆rH°) exothermicH-transfer (by H) 1010.4(RPD) 13.25 + 0.25∆rH° exothermicH-transfer (by R) 108.5(RPD/3) 16 + 0.65∆rH° endothermic

16 - 0.35(-∆rH°) exothermicH-transfer (by CH3) 1010.3(RPD) 13.7 + 0.75∆rH° endothermic

13.7 - 0.25(-∆rH°) exothermicH addition 1013.9(RPD/2) 6.52 + 0.113∆rH°decomposition C-H 108.5(RPD/3) 9.04 + 0.78∆rH° - RTdecomposition C-C 1014.0 20.00thermolysis 1015.5(RPD) ∆rH°

a RPD ) reaction path degeneracy.

E1 - E-1 ) ∆rH° - ∆nRT (E3)

ln( A1

A-1) )

∆rS°R

- ∆n[1 + ln(R1TC°P° )] (E4)

Table 3. Comparison between Experimental andSimulated Values

99 mol % of tetralin1 mol % of naphthalene

100 mol %of tetralin

compound(Xi/Xbut)

expt(Xi/Xbut)

simulated(Xi/Xbut)

simulated

methylindane 28.70 28.00 25.70naphthalene 3.34 6.30 0.65butylbenzene 1.00 1.00 1.00indane 0.63 0.50 0.86ethylbenzene 0.48 0.41 0.51toluene 0.13 0.10 0.26styrene 0.04 0.03 0.04propenylbenzene 0.03 0.03 0.04C20 0.85 0.80 1.15


initial mixture composed of 99 mol % of tetralin and 1mol % of naphthalene was chosen.

These authors presented their results using selectivi-ties (mol/100 mol reacted). With CHEMKIN II, we canonly calculate the molar fractions, so we have decidedto compare variations of the ratios X1-methylindane/Xnaphthahlene and Xnaphthahlene/Xbutylbenzene with time be-tween experimental and simulated values (Figure 4)using the mechanism described in Appendix 2.

We can conclude that we obtain a rather good agree-ment between the experimental and simulated valuesfor the major compounds. Concerning the minor com-pounds, no valuable values are available in the litera-ture.

Another test of our mechanism was performed bycomparing the global activation energy with the experi-mental activation energy found by Grigor′eva et al.10-12

under the same conditions: 14 MPa, 350-550 °C, anda conversion of tetralin of around 1%. The temperaturedependence of the rate consumption of tetralin is shownin Figure 5.

For the temperature range 360-450 °C, the calcu-lated global activation energy is equal to 57.6 kcal/mol,very close to the value of 59 kcal/mol found experimen-tally by Grigor′eva et al.10-12 between 350 and 500 °C.

Mechanistic Modeling Results

The model was used to elucidate the main reactionpathways in the pyrolysis of tetralin.

Flux Distribution. A simulation was performed at440 °C, 14 MPa, a residence time of 70 min, and 3%tetralin conversion. This simulation was studied indetail and was used to derive Figure 6, which showsthe various pathways through which products areformed.

Considering a flux of consumption of tetralin takenequal to 100, we calculated the overall flux of productionand consumption of the species involved. Arrows indi-cate the relative importance of fluxes. Numbers indicatethe relative importance of the different formationpathways (in bold type) or destruction pathways (initalics).

Routes of Formation of Different Compounds. UsingFigure 6, we can elucidate the main pathways leadingto the major compounds in the pyrolysis of tetralin.

1-Methylindane

Ninety percent of the 1-methylindane is formed byring contraction, and only 10% by intramolecular ad-dition.

Naphthalene

Naphthalene is only formed by dehydrogenation reac-tions.

Butylbenzene

Butylbenzene is mainly due to an ipso addition of aH atom on tetralin. Under those conditions, RHTreactions are insignificant.

Toluene

Ninety percent of the toluene is formed via an ipsoaddition of a H atom on 1-methylindane, and only 10%via H-transfer from butylbenzene.

Alkanes (CH4 and C2H6), Alkenes (C2H4 and C3H6),and Alkylbenzenes

Figure 4. Molar fraction ratios vs time compared with experi-mental data (ref 39) at 40 bar and 450 °C.

Figure 5. Pyrolysis rate of tetralin vs 1/T.


Alkanes and alkenes are due to the cracking of thebutylbenzene alkyl chain.

Kinetic Curves. A simulation was conducted at 450 °C,14 MPa, and a residence time of 8 h for neat tetralin.Figure 7 shows the kinetic curves for the decompositionof tetralin and for the formation of 1-methylindane,n-butylbenzene, and naphthalene.

The primary products are 1-methylindane and n-butylbenzene. The amounts of these products passthrough a maximum. 1-Methylindane is decomposedinto indane, whereas n-butylbenzene is decomposed intotoluene, ethylbenzene, styrene, propenylbenzene, al-kanes, and alkenes. Naphthalene is a secondary product

whose concentration grows steadily with tetralin con-version. Note that, at high conversion, the model resultsare probably less reliable than they are at low conver-sion, because of additional reactions that doubtless takeplace and have not been included in the model.

Temperature Effect. Different simulations wereperformed to study the effect of temperature on theconversion of tetralin. Starting from 99 mol % of tetralinwith 1 mol % of naphthalene at 14 MPa, we studied thereaction residence necessary to obtain 30% tetralinconversion at 300, 400, 500, and 600 °C (Figure 8).Figure 9 shows the curves of formation of the mainproducts.

Figure 6. Diagram of radical transformations of tetralin at 400 °C, 13.9 MPa, 70 min, and 3% tetralin conversion.


We can observe that the molar ratio of 1-methylin-dane decreases when the temperature increases, whereasthose of n-butylbenzene and naphthalene increase withtemperature. The same results have been found experi-mentally by Yu and Eser.39 In Figure 10, we comparevariations in the ratios X1-methylindane/Xnaphthahlene andXnaphthahlene/Xbutylbenzene with temperature between ex-perimental and simulated values at 40 bar and aconversion of around 6%. In conclusion, the model givesa good representation of the variations of the mainproducts with temperature.

Importance of Impurities. A series of simulationswas performed to compare the rate of tetralin pyrolysisusing neat tetralin, tetralin with 1 mol % of dihy-dronaphthalene, and tetralin with 3 mol % of dihy-dronaphthalene at 440 °C, 14 MPa, and a residence timeof 4 h. We obtained the results depicted in Figure 11.This figure emphasizes the importance of the knowledgeof the level of impurities in the tetralin used for anyexperiment.

Case of RHT. In Appendix 2, we notice that RHTreactions are another means of forming products suchas naphthalene, dihydronaphthalene, and alkenes. With

the support of flux calculations (Figure 6), we canconclude that, under our conditions, RHT reactions arenegligible. Indeed, the rate of production of this productthrough the reactions written above is around 1 × 10-10

mol cm-3 s-1 compare with 1 × 10-13mol cm-3 s-1 forRHT reactions.

Figure 7. Kinetic curves for the decomposition of tetralin andfor the formation of 1-methylindance, n-butylbenzene, and naph-thalene (450 °C, 14 MPa).

Figure 8. Time to reach 30% conversion of tetralin.

Figure 9. Formation of 1-methylindance, naphthalene, andn-butylbenzene as a function of tetralin conversion at differenttemperatures.

Figure 10. Ratios of molar fractions vs temperature comparedwith experimental results (ref 39) at 40 bar and around 6%conversion.


Chain Length λ. The kinetic chain length λ28 is definedas the rate at which radicals propagate the chain toproduce product molecules relative to their rate oftermination. The latter is also equal to the rate ofinitiation (quasi steady-state approximation). Hence

At 440 °C, 14 MPa, and a residence time of 70 min, for99 mol % of tetralin plus 1 mol % of naphthalene, thechain length λ is 5. This low value means that thethermal transformation of tetralin is mainly controlledby initiation reactions.

Conclusion

A mechanism consisting of 132 free-radical reactionshas been written to describe the pyrolysis of tetralin.This mechanism has been validated using the experi-mental results of Khorasheh and Gray,13 Yu and Eser,39

and Grigor′eva et al.10-12 A chemical analysis has beenmade from this model and leads to the followingconclusions: (i) The chain length is low and equal to 5(440 °C, 14 MPa, 70 min). (ii) Tetralin pyrolysis is verysensitive to impurities; the knowledge of the impuritylevel in the tetralin used for any experiment is thus veryimportant in interpreting its kinetics. (iii) RHT reactionsare insignificant under our conditions. (iv) The produc-tion of 1-methylindane is due to ring contraction. (v) Theproduction of naphthalene is due to dehydrogenationreactions. (vi) The production of butylbenzene is due tothe ipso addition of a hydrogen atom to tetralin. (vii)The production of toluene is due to the ipso addition ofa hydrogen atom to 1-methylindane, followed by adecomposition reaction. (viii) Alkanes and alkenes aremostly due to the cracking of the alkyl chain of n-butylbenzene. (ix) The formation of 1-methylindanedecreases when temperature increases, whereas thoseof n-butylbenzene and naphthalene increase with tem-perature.

In a future work, we will analyze the effects ofH-donors (such as tetralin) on the pyrolytic decomposi-tion of long-chain alkanes such as n-hexadecane bystudying the binary mixture of tetralin and n-hexade-cane. We will examine the inhibiting effect of tetralinon the decomposition of n-hexadecane by using adetailed radical mechanism with kinetic data in Arrhe-nius form, and we will also compare the inhibiting effectof tetralin with that of a well-known H-donor, namely,toluene.

Acknowledgment

This work was supported by ELF-Exploration-Pro-duction (Pau-France). We thank the reviewers for theirhelpful comments.

Appendix 1: Estimation of Aryl-AlkylCarbon-Carbon Bond Dissociation Energy inTetralin

Units ) kcal/mol

Dcφ-c1 ) aryl-alkyl carbon-carbon bond dissociationenergy

Dcφ-h ) aryl carbon-hydrogen bond dissociationenergy

Dc-h ) alkyl carbon-hydrogen bond dissociationenergy

∆rH° ) enthalpy of reaction∆fH° ) enthalpy of formation of a speciesTo estimate the aryl-alkyl carbon-carbon bond dis-

sociation energy we have to calculate ∆rH° of thereaction above.

∆rH°(tetralin) ) 6.2 (see Appendix 3)To evaluate ∆fH°(compound 1), we use the reaction

∆fH°(butylbenzene) ) -3.1 (see Appendix 3)∆fH°(H•) ) 52.1 (see Appendix 3)Dcφ-h ) 111 (Berkowitz et al.,40 1994)Dc-h ) 99.5 (Berkowitz et al.,40 1994)

Then

Then

Figure 11. Conversion of tetralin vs time (440 °C, 14 MPa).

λ ) rate of propagationrate of initiation

(E5)

∆rH°A ) ∆fH°(compound 1) - ∆fH°(tetralin) )Dcφ-c1

∆rH°B ) ∆fH°(compound 1) + 2∆fH°(H•) -∆fH°(butylbenzene) ) Dcφ-h + Dc-h

∆rH°B ) 111 + 99.5 ) ∆fH°(compound 1) + 2 ×52.1 + 3.1

∆fH°(compound 1) ) 103.2

∆rH°A ) Dcφ-c1 ) 103.2 - 6.2 ) 97.0 soDcφ-c1 ) 97.0 kcal/mol


Appendix 2: Mechanism of ThermalTransformation of Tetralin


Appendix 3: Enthalpies of Formation andEntropies of Some Species Involved in theReaction Mechanism


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Received for review February 28, 2000Revised manuscript received July 24, 2000

Accepted August 16, 2000

IE000276F


mechanistic modeling of the thermal cracking of tetralin

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