Ind. Eng. Chem. Process Des. Dev. 1981, 20, 379-384
method. Analysis of this solid showed no other compound present except for the original dibenzothiophene. No chlorine was detected in the product. Thus, the chloride ion was not active in the conversion of DBT to DBT02. Conclusion Because the dibenzothiophene in an aqueous system can be quantitatively oxidized by chlorine to the sulfone, it is expected that the dibenzothiophene structure in fuel oil and coal can be similarly oxidized with a minimum of attack of other atoms by the chlorine. That result suggests that the oxidation of the sulfur then would be accompanied by relatively minor losses of heating value. Even though the sulfur is quantitatively oxidized, desulfurization requires an additional step to split out the sulfone structure. Acknowledgment Work reported here was part of a program receiving support from the Department of Energy, the Beaumont
579
Foundation, the National Science Foundation, and the Bechtel Corporation. The support is gratefully acknowledged. Literature Cited Attar, A.:Corman, W. ti. Id.€ng. Chem. prod. Res. Dsv. 1078, 17, 102. Bedocchi, E.; Mandollnl, L. Rlc. scl. 1067, 37, 863. Brown, R. K.: CMstlansen. R. G.; Sandln, R. B., J . Am. Chem. Suc. 1048, 70, 1748. Dronov, V. I.; Lebedeva, M. N.: Enkeev, R. S.; Krles, E. A. "Chemistry of Organlc Sulfv Compounds In Petroleum and Petroleum Products", Akademlya Nauk SSSR, Vd. VI, 1964. (Tranelated from Rwlan, Jeruealem, 1967, p 316). Dronov, V. I., Kundryutskaya, N. N.; Prokhorov, (3. M.; Enkeev, R. S.; Vallt* va, G. 2. Khkn. Sereorg. soedn., m r z h . Ne?tyakh Nelbprod, 1972, 8 , 158: Chem. ~ b s t r 1978, . 79, 115388f. Flks. K.; Vogt, W. Ann. 1011, 387, 341. Reld, E. E. "Organic Chemlstry of Bhralent Sulfw", Vd. 11, Chemlcal PubllshIng CO.: New York, 1960; p 48.
Received for review February 25, 1980 Accepted December 22, 1980
Hydrodealkylation of I-Ethylnaphthalene and Its Side Reactions. A Kinetic Study Paolo Beltrame' and Paolo Carnltl Istituto di Chimica Fisica, UniversitS, 20 133 Milano, Ita&
Bruno Maronglu, Lulgl Mura, and Vlncenro Sollnas Istituto Chimico, UniversitS, 09 100 Cagliari, Italy
Sandro Mor1 Euteco Impianti S.p.A., 20 lgl Milano, Italy
The thermal hydrodealkylation of l-ethylnaphthalene (AEN) has been studied in a tubular flow reactor, at effective reaction temperatures in the range from 550 to 660 OC. Total pressure ranged from 4 to 40 atm, and HP/ hydrocarbon molar ratio in the feed was varied from 3 to 9. Main products were naphthalene (N), l-methylnaphthalene (AMN), acenaphthene (A), and acenaphthylene (AA). The latter is the product of a dehydrogenation which is strongly depressed at pressures of 20 atm or higher. Kinetic resutts in the high-pressure region have been interpreted according to a scheme of three parallel reactions of AEN (to AMN, N, and A, respectively) besides a further reaction of AMN (to N), assumlng rate equations of the form r = ItGmG. Arrhenius parameters and reaction orders were obtained that reproduce experlmental molar conversions *1b% on the average.
Reaction products and kinetics of the thermal hydrodealkylation of 1- and 2-methylnaphthalene and of 2ethylnaphthalene have been studied previously (Beltrame et al., 1975, 1976, 1979). Both ethylnaphthalenes are interesting as models of the higher alkylnaphthalenes that can be employed in industrial applications. Therefore the study has been extended to the 1-ethyl isomer (AEN) and results are presented here. Experimental Section Materials. 1-Ethylnaphthalene was a Fluka pure (>99%) product. Acenaphthene (95%) and acenaphthylene (98%) were Fluka practical products; the former was re0196-4305/81/ 1 120-0379$01.25/0
crystallized from aqueous ethanol to gas chromatographic purity. 1-Vinylnaphthalene(AVN) was a Fluka technical product. 1-Ethynylnaphthalenewas prepared from AVN by bromination and alkaline dehydrobromination; the product was a mixture in which 1-ethynylnaphthalenewas identified by GC-MS. Cylinder 99.99% hydrogen was employed. Apparatus and Procedure. They were as described by Beltrame et al. (1975, 1979). The axial temperature profile measured along the reactor showed a large central portion with roughly constant temperature (f10 "C) and lower values in the entrance and exit regions. An effective reaction temperature (Teff)was defined for each run by 0 1981 American Chemical Society
380
Ind. Eng. Chem. Process Des. Dev., Vol. 20, No. 2, 1981
Table I. Estimated Equilibrium Constants (atm) for Dehydrogenation Reactions 4 and 6 reaction temp, K 4a 4b 6b 6c
800 900 1000
0.047 0.38 2.0
0.040 0.32 1.7
39 106 235
>25
Values calculated from thermodynamic data (Stull e t al., 1969)for the benzene analogues of the naphthalenic compounds. Values estimated by the method of group contribution (Benson, 1968). From experiments.
considering the length of the reactor (zefi) where temperature was within 40 "C of its maximum value and taking the arithmetic mean of the measured temperatures along it. Reaction Products. Many condensed products were known and their determination by GC analysis was effected in the conditions of previous works (column 2.5 m long packed with 3% SE-52 on Chromosorb W-DMCS). Specific products of the present study were identified by GC-MS as compounds of mol wt 152 and 154. Since acenaphthene and 1-vinylnaphthalene both have mol wt 154, while acenaphthylene and 1-ethynylnaphthalene have mol wt 152, samples of all four compounds were examined. The peaks of mol wt 152 and 154 in the reaction products were ascertained to be acenaphthylene and acenaphthene, respectively. However, the accurate determination of retention times revealed that, in the conditions of the standard GC analysis, AVN gives a shoulder on the AEN peak which is difficult to detect and even more to measure separately. A good separation was achieved on a capillary column (50 m), filled with SE-54; AVN proved to be present in the reaction products in amounts smaller than those of acenaphthylene, which is itself a relatively unimportant product. Therefore the standard GC analysis was left unchanged, giving up the idea of measuring AVN and accepting a small error in the determination of AEN. Summing up, the main condensed products were found to be naphthalene, 1-methylnaphthalene, acenaphthene, and acenaphthylene. Among minor products a few (benzene, toluene, binaphthyls) were identified, but a detailed study was not undertaken. In terms of naphthalene rings (or benzene rings derived from them) the composition of the reaction products was main products 197%, byproducts 1 3 % . In the gaseous phase, methane and ethane were the main products; ethylene was present in amounts at least one order of magnitude smaller than those of ethane. Exact gas analyses were not performed. Results Kinetic runs were carried out at various total pressures from 3.9 to 39.7 atm. The hydr0gen:hydrocarbon molar ratio in the feed (RH) ranged from 3 to 9. Hydrocarbon feed rates were in the range 0.1-0.4 mol/h. Analyses of the condensed reactor effluent always revealed considerable amounts of unreacted AEN, naphthalene (N), 1-methylnaphthalene (AMN), and acenaphthene (A). In the lower pressure runs acenaphthylene (AA) was also of some importance, while at higher pressure it was negligible. 1-Vinylnaphthalenewas detected in small amounts. The following stoichiometric equations may be written to account for the observed main products of the lowpressure runs. CioH,C2H5 + Hz C10H7CH3 + CHI (1) C,oH,CH, + Hz CloHB + CHI (2)
-
(3)
CH=CHz
CH =CH
@=@@I+'. While reactions 1to 5 are analogous to thoses proposed in the case of 2-ethylnaphthalene (Beltrame et al., 19791, other reactions are specific for the 1-substituted naphthalene, because they involve ring closure on the peri position. Hydrodealkylations 1-3 and 5 have been written above without the reverse reaction, because the thermodynamic estimates made for 2-substituted naphthalenes are equally valid in the present case. On the contrary, the reverse reactions have been explicitly indicated for dehydrogenations 4 and 6-8. In fact, the reverse reactions would be in any case negligible only if K,/pH, were >>1,that is for Keq >> pH2.Since, for some of the molecules involved, thermodynamic data are not available to us, values of K, could not be calculated. Estimates were attempted for reactions 4 and 6, with the results shown in Table I: the equilibrium constant appears to have low values for reaction 4, while the case of reaction 6 is probably borderline. A t sufficiently high hydrogen partial pressure, dehydrogenations should be shifted to the left side and therefore negligible, together with their consecutive reactions. In these conditions, one would be left with the simplified kinetic scheme including only reactions 1-3. In our experimental pressure range this condition was not achieved, because even in the high-pressure runs (20-40 atm) acenaphthene was observed as one of the main products. Therefore, moving from the pressure range 4-10 atm to the range 20-40 atm is actually critical for reaction 4 (and subsequent reactions 5 and 7) and for reaction 8, which also must have a relatively low equilibrium constant, but not for dehydrocyclization of AEN (eq 6), which is far for equilibrium in the conditions (hydrogen partial pressure, temperature, and residence time) of experimental runs. The position of equilibrium for reaction 6 was further checked by experiment. Runs at an effective temperature of ca. 900 K ( P = 20.4 atm; RH = ca. 7) with a feed containing AEN + A (€020in moles), showed that the fraction of acenaphthene in the effluent was an increasing function of retention time. Equilibrium was not even approximately approached and only a lower limit of the equilibrium constant was obtained, that is Keq> 25, as reported in Table I. Feed compositions more rich in acenaphthene were difficult to handle because of their higher melting point. Anyway, the experimental result is in qualitative agreement with the estimated values of Kq. The overall picture (rather large K,, equilibrium position never approached, conversion not depressed by high pH2values) suggested that, as a reasonable approximation, the reverse reaction of 6 could be just neglected. Therefore
Ind. Eng. Chem. Process Des. Dev., Vol. 20, No. 2, 1981 381 Table 11. Kinetic Results of High-Pressure Runs molar conversions group of runs
D
E
Teff,
C
zeff, cm
feed rate of AEN mol/h
9.0 8.3 9.0 8.7 3.0 3.0 3.3 3.0
628 631 635 630 620 625 619 626
40.6 40.0 40.7 41.8 48.2 44.0 46.4 47.8
0.194 0.258 0.323 0.387 0.136 0.194 0.258 0.387
6.7 6.7 7.0 7.O 7.0 7.0 7.3 7.5
592 597 585 59 6 594 623 734 625
41.2 43.2 47.8 42.5 43.0 46.6 43.7 44.5
0.129 0.194 0.258 0.323 0.387 0.194 0.323 0.387
6.4 7.6 6.9 6.3 7.3
554 556 557 55 1 558
41.3 40.2 37.8 38.5 38.2
0.136 0.194 0.258 0.336 0.368
RH
YM
YN
exptl calcd (P = 20.4 atm) 0.13 0.12 0.16 0.13 0.14 0.12 0.10 0.11 0.29 0.28 0.26 0.29 0.20 0.24 0.22 0.25
YA
exptl
calcd
exptl
calcd
0.31 0.27 0.31 0.25 0.35 0.29 0.21 0.21
0.36 0.31 0.27 0.21 0.46 0.36 0.27 0.21
0.11 0.11 0.11 0.09 0.11 0.11 0.09 0.09
0.09 0.09 0.09 0.07 0.13 0.12 0.10 0.10
0.10 0.11 0.07 0.08 0.07 0.14 0.15 0.12
0.25 0.26 0.19 0.18 0.16 0.44 0.43 0.36
0.43 0.34 0.22 0.21 0.17 0.49 0.39 0.28
0.06 0.06 0.05 0.05 0.05 0.10 0.11 0.09
0.09 0.08 0.05 0.06 0.05 0.16 0.16 0.11
( P = 39.7 atm) 0.04 0.05 0.05 0.04 0.03 0.03 0.03 0.03 0.02 0.02
0.25 0.18 0.19 0.10 0.13
0.28 0.21 0.16 0.11 0.11
0.03 0.02 0.03 0.02 0.02
0.04 0.03 0.02 0.02 0.02
(P=30.0atm) B
C
A
0.10 0.09 0.05 0.07 0.05 0.17 0.16 0.12
Table 111. Measured Conversions in Low-Pressure Runsa feed rate group of T$ff of AEN runs RH C mol/h
molar conversions
9
YM
YN
YA
YAA
(P= 3.9 atm) I
8.6 9.0 9.0 9.2 8.9
662 661 662 660 660
0.129 0.194 0.258 0.323 0.387
0.19 0.13 0.12 0.10 0.09
0.29 0.27 0.23 0.18 0.17
0.14 0.13 0.10 0.12 0.11
0.09 0.08 0.07 0.06 0.04
G
7.0 6.9 7.0 7.0 6.4
657 659 663 657 660
( P = 5.8 atm) 0.136 0.21 0.194 0.19 0.258 0.18 0.323 0.13 0.387 0.15
0.32 0.28 0.24 0.22 0.19
0.15 0.14 0.14 0.13 0.12
0.07 0.07 0.06 0.04 0.04
F
6.4 6.9 6.8 7.0 6.9
629 631 632 629 632
0.142 0.194 0.258 0.323 0.387
0.25 0.23 0.21 0.18 0.18
0.12 0.12 0.10 0.10 0.10
0.02 0.02 0.01 0.01 0.01
(P= 9.7 atm)
a
0.18 0.14 0.13 0.10 0.09
Values of z e (cm): ~ 44 t 1 (group I), 41 t 1 (G),43 k 3 (F).
the high-pressure runs were interpreted within the following simplified kinetic scheme (omitting gases).
(9) A
Reaction scheme 9 accounts, on the average, for 98% of the reaction product for 21 runs carried out at a total pressure above 20 atm (poH,> 15 atm). In these cases, therefore, analyses were normalized to four components (AEN, AMN, N, A), and molar conversions of AEN to AMN ( y ~ )to , N (yN),and to A (y.J were evaluated for each run. Results are shown in Table 11. Detailed results of
gas chromatographic analyses are given in the Appendix. At lower pressure ( P < 10 atm; p q < ~ 8.5 ~ atm) acenaphthylene (AA) was no longer negligible and was considered in addition to the previous products. In this way 99% of the reaction product is accounted for, on the average. Analyses normalized to five components (AEN, AMN, N, A, and AA) were used to evaluate separate conversions of AEN to AMN (YM),N (yN), A CY*), and AA (yU) for each run. Values are given in Table 111. Kinetic calculations were performed only for the highpressure runs according to reaction scheme 9. As in previous works (Beltrame et al., 1975,1979), the fluid motion in the annular reactor was treated as laminar. By an approximate method, the reactor was considered as the sum of four segregated plug-flow reactors, characterized
382 Ind. Eng. Chem. Process Des. Dev., Vol. 20, No. 2, 1981
by different values of the fluid velocity, according to a procedure for the partition of the gas flow into cylindrical coaxial crusts (Carniti et al., 1979). The rate equations 10-12 were written as for a constant volume process. Actually reaction 6 involves molar expansion, but YA values (Table 11) are so small that the volume change of the system during reaction does not exceed 2-3% in the worst case.
Table IV. Kinetic Parametem for Rate Eq 10-12 (k = ~ . e - E / 1 . 9 8 7 . T )
A , s-' E, reaction (mol/L)l"" kcal/mol la 8.6 X 10" 56.2 2b 4.8 x io9 50.8 3c 3.7 x 103 25.0 6' 1.9 X lox4 65.1
m
n
1.0 0.25 0.25 1.0
0.0 0.80 0.80 1.0
a Standard deviations: A 0.5 for log A , i 2 kcallmol for Parameter values from a previous work (Beltrame E. et al., 1975). Standard deviations: ~ 0 . for 8 log A , * 3 kcal/mol for E.
therefore, considering that &,is a function both of T and of CH, according to eq 17, the best interpolating plane of E6
In the pseudo-isothermal approximation kl,kz, k3, and k6 are meant as kinetic coefficients at the effective temperature (Ten)of the reactor. Since hydrogen is an excess ceagent, its concentration can be taken as the average (CH) of entrance and exit values. The latter was estimated by the formula
where the coefficient 1.5 of YN in the numerator is the average of the limit values, were naphthalene only produced through reactions 1-2 (value 2) or only by reaction 3 (value 1). This is an arbitrary choice, but has little numerical consequence. Under these approximations, hydrogen concentration may be incorporated into kinetic coefficients defined as K1 = k 1 Q , etc., and rate equations 10-12 rewritten as -~
dt
AEN
+ K3C,;
+ K&GN
(14)
In & = In A6 - - + n6 In C H ~ RT In K6 vs. l/Teff and In was calculated by the leastsquares procedure, obtaining n6. Such value, close to 1, was rounded off to n6= 1, and this allowed us to calculate k6 for each run. Arrhenius plots were drawn for kl,k3,and ke, considering for each run its TeBvalue. Reaction orders and Arrhenius parameters for the various reactions are summarized in Table IV. By using kinetic coefficients obtained from the Arrhenius equations one can calculate molar conversions yM, YN, and YA to be compared with the experimental values. This may be done either (a) within the previous approximations (CH~,zeff, and Teffvalues) or (b) removing the approximations. For case (b) a further differential equa~ as a tion (18) was added to eq 10-12 and C Hconsidered
- -dCHz - -
dt klC"lCml
Hz AEN
where C-N = Co" - CAEN - CN - CA, and dependent variables are C", C N , and CA. For the determination of kinetic parameters, large use has been made of previous results concerning AMN and 2-ethylnaphthalene (BEN) (Beltrame et al., 1975, 1979), so we knew values of k,, n,, and m2,and their confidence limits; furthermore, assuming a strict analogy between AEN and BEN, it was taken that m l= 1; nl = 0; m3 = m2; n3 = n2. Dehydrogenation 6 was considered as first-order with respect to the hydrocarbon, that is m6 = 1. As to the remaining unknowns in eq 14-16, that is K1, K3,and &, they were obtained by the method previously applied to BEN. In short, concentrations of AEN, N, and A at the reactor outlet were calculated through (i) integration of the differential equations by the Runge-Kutta method for each segregated reactor portion and (ii) weighted average of the results. Coefficients K1,K3, and K6 for each run were such as to make calculated concentration values equal to the experimental ones, obtained from the corresponding molar conversions (Table 11). The next stage was the calculation of coefficients kl, k3, and k6 from K1, K3, &, and values of This was easily done, for each run, in the case of kl, and k3, since values of nl and n3 were available. In the case of reaction 6, an isothermal set of runs at different hydrogen concentrations would have_allowed the evaluation of n6 from a plot of In K6 vs. In C H ~ .However, such a set was not available;
+ k2CZ2CFMN+ k3Cn3Cm3 - k & ~ z c(18) ~~N Hz AEN
dependent variable, in addition to C", CN, and CA; moreover, the actual temperature profiles along the reactor were employed. Mean square deviations of calculated from experimental conversions were evaluated by both methods, obtaining: for YM, (a) 0.016 and (b) 0.018; for YN, (a) 0.055 and (b) 0.062; for YA, (a) 0.020 and (b) 0.021. Therefore the kinetic parameters obtained by the pseudo-isothermal approximation are about equally good in interpreting experimental results when the approximations are removed. Taking into account the different levels of YM, YN, and YA values in kinetic runs, on the average the relative deviations (method b) are about 15% for yM, 24% for YN, and 30% for YA, and 18% for overall conversion. Values calculated by method b are given in Table I1 for comparison with experimental values. The entire procedure was also applied in parallel calculations which treated the fluid motion in the reactor within the plug-flow approximation. This could be a better model if the radial concentration profile were made uniform by diffusion effects. However, a worse agreement between calculated and experimental conversions was obtained using the plug-flow model, both in case (a) and in case (b). In particular, this model does not improve the fitting of the data at low flow rates. Discussion The approximation of treating the reactor as pseudoisothermal, by introducing an effective length and an effective temperature, successfully experienced for 2ethylnaphthalene, was considered convenient also in the present case, which includes, even in the simplest ap-
Ind. Eng. Chem. Process Des. Dev., Vol. 20, No. 2, 1981 383
Table V. Gas Chromatographic Analysis of Condensed Products ("01) (Listed in the Same Order as in Table 11) groupof runs
AEN fed
AEN
AMN
N
D
64.53 64.53 80.67 70.99 67.76 64.53 64.53 64.53 53.76 64.53 64.53 80.67 64.53 64.53 80.67 64.53 67.76 64.53 64.53 83.89 61.31
28.60 28.55 33.46 36.51 15.33 20.41 32.46 29.37 28.98 36.48 41.43 54.55 43.37 17.38 22.12 26.12 41.97 45.03 48.14 64.19 46.79
8.43 10.16 10.41 6.68 17.57 15.63 13.27 13.35 4.73 5.92 2.92 5.30 2.82 9.90 11.54 7.72 2.76 3.22 1.75 1.95 1.26
19.63 17.10 23.29 16.03 21.73 17.59 13.98 12.70 12.39 16.64 10.71 14.46 9.21 26.40 31.04 22.64 15.26 10.80 11.81 7.25 7.52
E
B
C A
a
for High-pressure Runs other products
A
0.53 0.65 0.82 0.46 0.69 0.79 0.63 0.59 0.09 0.12 0.09 0.17 0.10 0.53 0.89 0.55 0.12 0.09 0.13 0.11 0.08
6.76 6.87 7.98 5.74 6.91 6.77 6.15 5.77 2.79 3.77 2.66 4.25 2.66 6.23 8.24 5.79 1.75 1.36 1.60 1.27 1.19
dinapht hyls
0.06 0.08 0.08 0.05 0.18 0.16 0.05 0.11 0.04 0.04 0.02 0.08 0.02 0.13 0.16 0.14
With retention times in the regions of benzenic and naphthalenic compounds.
proximation (reaction scheme 9), four parallel-consecutive reactions. Results show that for reactions at high prmure, to which reaction scheme 9 could be applied, kinetics are fairly well interpreted using parameters obtained under the pseudo-isothermal approximation, even after removing such approximation. A comparison of experimental and calculated conversions is usually more convincing when it is in graphical form, typically as a plot of such conversions vs. residence time for a series of otherwise similar runs. In our case, this presentation requires some loss of accuracy, since in each group of runs there are, besides regular variations of residence time, random oscillations of other parameters, that is T&,z,R, and RH. Only by taking average values of these parameters, calculated curves of conversions vs. residence time can be obtained and compared with the experimental points. An example is shown in Figure 1. The agreement is good, taking into account the approximations. The point of neglecting the reverse reaction of (6) has already been discussed. It can be added that calculations including such reaction have also been performed, modifying in the appropriate way eq 12 and 16 and using tentative values of the equilibrium constant, as far as possible from the approximation of scheme 9, that is close to the experimental limit at 900 K. The temperature dependence foreseen by the method of group contribution = 13.6 kcal/mol, well was accepted, since it gives AHo298 comparable with the reported value 14.3 kcal/mol (Stull et al., 1969). These computations gave kinetic parameters almost equal to those obtained under the approximation of reaction scheme 9, for reactions 1-3, and slightly different only as far as reaction 6 was concerned. Fitting of calculated to experimental yAvalues was somewhat improved but not enough to justify the use of an equilibrium constant arbitrarily chosen or estimated with uncertainty, due to the presence of polycyclic rings. I t may be mentioned that the method of group contribution, as applied by Khalima-Mansur et al. (1973), was reported to give, for the equilibrium constant of reaction 6, extremely low values, for instance 6.46 X lo4 atm at 900
I
0.5
i
'I .
/-
I
Figure 1. Molar conversions vs. residence time for runs of group A. Curves were calculated for the average conditions of the group (TeR = 555 K;RH = 6.9;zeff = 39 cm).
K, in disagreement with experimental results and with our estimates by the same method. Calculations for reaction 4 by the same authors (Khalima-Mansur et al., 1973) gave results close to ours: for instance, 0.16 atm at 900 K, against values 0.32 and 0.38 shown in Table I from two different estimates. Because the present kinetic treatment is heavily dependent on a previous determination of reaction orders n2 and m2,it was felt convenient to vary their values (and consequently that of k2)within their known confidence limits. However, no improvement of the fitting was obtained. The presence of little or no acenaphthylene (AA)in the high-pressure runs is justified by a shift of equilibrium 8 to the left. In such situation, if reaction 7 has a large enough equilibrium constant, there could still be formation of AA from AVN by such a reaction, provided AVN were available in the system in sufficient concentration. Clearly this is not the case, since a high hydrogen pressure shifts equilibrium 4 to the left. In the runs of Table I11 pressure was lower and often temperature was higher: this favored the formation of
384
Ind. Eng. Chem. Process
Des. Dev., Vol. 20, No. 2, 1981
acenaphthylene in appreciable, although still modest, amounts, as observed particularly in runs at 3.9 and 5.8 atm. Both A and AA behaved as final reaction products and not as intermediates, with concentrations (see YA and y u values) continuously increasing with residence time. Therefore there was no kinetic evidence of hydrocracking of the five-membered ring of acenaphthene, although in general this reaction is reported (Asselin, 1964). 1Vinylnaphthalene was probably behaving as an intermediate, produced by reaction 4 and subjected to reactions 5 and 7, but unfortunately it could not be systematically analyzed. Anyway, some ethylene was detected in these low-pressure runs, making it evident that reaction 5 was also contributing to the production of naphthalene. The trend of YM as a function of residence time (Tables I1 and 111)is only rarely characterized by a maximum such as expected for a reaction intermediate. As shown by the calculated YM values, at longer residence times such a maximum would have been more apparent. Among kinetic parameters, most have values in the expected range, taking previous results into account. The low value of the activation energy for reaction 3 is anomalous; cumulative errors may have affected this temperature-dependence determination. Also, the value 1for n6 (reaction order with respect to hydrogen) is surprising, since zero would seem a more reasonable value for a dehydrogenation. Anyway, only an empirical significance is attached to kinetic equations (10-12) and to their parameters. They are considered to be of practical value, since they have been determined in a range of temperature, pressure, and Hz:hydrocarbon ratio suitable for design purposes. Overall conversion of AEN in some cases was over 70%. The importance of A in a practical reaction product, obtained under high pressure and at large conversion, might be less than foreseen by the kinetic model: indications of this are given by runs of group C (Table 11). Having completed the kinetic study of hydrodealkylation of methylnaphthalenes and ethylnaphthalenes, several comparisons of rates are possible. Within reaction scheme 9, the reactivities of AEN and AMN to give naphthalene in a direct way can be evaluated observing k3 and kz values, respectively. At 600 "C they are (Table IV): k3 = 20.5 X k z = 9.1 X lo4 Lo.o5m o P o 5s-l; therefore AEN is 2.3 times more reactive than AMN (BEN was found to be 2.8 times more reactive than BMN at the same temperature). Partial dealkylation, in the reaction from ethyl- to methylnaphthalene, is characterized by kl = 7.3 X s-l at 600 "C in the case of 1-isomers (Table IV). A value of kl = 4.0 X W3s-l can be calculated for the 2-isomers at same temperature from previous results (Beltrame et al., 1979). AEN appears to be 1.8 times more reactive than BEN in this reaction. In the direct dealkylation to naphthalene, AEN and BEN cannot be compared by their kinetic coefficients,
because reaction orders are slightly different. A comparison is possible in terms of reaction rates in suitable chosen "standard conditions" such as pH2= 15 and PEN = 3 atm, temperature 600 "C. Rates calculated from the parameters of Table IV and of the previous work (r3 = k3C28C3$ are r3(AEN) = 0.266; r&BEN) = 0.221 mmol L-' s-l. The 1-alkyl isomer was found to be more reactive than the 2-alkyl one also in the case of methyl derivatives (Beltrame et al., 1975). I t can be concluded that 1-ethylnaphthalene appears from our measurements to be in every respect more reactive than the previously examined alkylnaphthalenes in hydrodealkylating conditions. Appendix Analytical Detail. For each run, a given amount of AEN was fed a t the appropriate flow rate and the condensed product collected during the same time. Unreactd AEN and different products, as analyzed by GC, were found in the molar amounts given in Table V, where moles of AEN fed are also shown. Nomenclature A = Arrhenius frequency factor (mol/L)'+"/s C = molar concentration of j , mol/L E/ = Arrhenius activation energy, cal/mol k = rate coefficient, (mol/L)'+""/s K = rate coefficient, (mol/L)'-"/s Kq = equilibrium constant m = reaction order with respect to hydrocarbon n = reaction order with respect to H2 P = total pressure, atm pj = partial pressure of j , atm r = reaction rate RH = (H2/hydrocarbon) feed molar ratio t = residence time, s T = temperature, K y j = molar conversion to product j z,ff = effective reactor length, cm Superscripts 0 = inlet value of variable f = outlet value of variable Literature Cited Asselin. G. F. A&. Pet. Chem. Refin. 1964, 9 , 72. Beltram, P.; Maronglu, B.; Solinas, V.; Torrazza, S.; Forni, L.; Mori, S. Ind. Eng. Chem. procesS Des. Dev. 1975, 14. 117. Beltrame, P.; Cavain, L.; Landone, A.; Marongiu, B.; Solinas, V.; Torrazza. S. Chim. Ind. (Milan) 1976, 58, 163. Beitrame, P.; Carniti, P.; Marongiu. B.; Mura, L.; Solinas, V.; Mori. S.; Ind. Eng. Chem. Process Des. Dev. 1979, 18, 336. Benson, S. W. "Thermochemical Kinetics"; Wiley: New York, 1968; Chapter 2. Carniti, P.; Mori, S.; Tassara, A.; Forni, L. Ing. Chim. Ita/. 1979, 15, 13. Khallma-hlansur, A.; Erivanskaya, L. A.; Plate, A. F. Pet. Chem. USSR 1979. 13. 229. Stuil, D. R.; Westrum, E. F., Jr.; Slnke. G. C. "The Chemical Thermodynamics of Orgenlc Compounds"; Wiiey: New York, 1969.
Received for review January 30,1980 Accepted December 16, 1980
