Kinetics of the HDN of Quinoline under Vapor-Phase Conditions

Department of Chemical & Fuels Engineering, University of Utah, Salt Lake City, Utah 84112. Ind. Eng. Chem. Res. , 2003, 42 (5), pp 1011–1022. DOI: ...
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Ind. Eng. Chem. Res. 2003, 42, 1011-1022

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Kinetics of the HDN of Quinoline under Vapor-Phase Conditions F. E. Massoth* and S. C. Kim Department of Chemical & Fuels Engineering, University of Utah, Salt Lake City, Utah 84112

Four extended runs, employing a CoMo/Al2O3 catalyst or a NiMoP/Al2O3 catalyst, were made with quinoline or decahydroquinoline as the feed to determine the kinetics of the vapor-phase hydrodenitrogenation (HDN) of quinoline at 613 K and 3.4 MPa. The data indicated appreciable inhibition of HDN by N-containing intermediates. Langmuir-Hinshelwood rate equations of the HDN network were used to fit the experimental data. It was necessary, first, to subdivide the network into smaller groups of certain species to obtain reasonable parameter values, which were then employed as estimates in the complete network. Three different types of active sites were required to achieve satisfactory fits to the data. It was found that an additional reaction path was also needed in the case of the CoMo catalyst that is not included in the usual HDN network. Propylbenzene was a minor product and was formed mainly from the dehydrogenation of propylcyclohexene. The CoMo catalyst was more active than the NiMo catalyst for the HDN of quinoline. Introduction Quinoline has long been considered to be representative of six-membered, heterocyclic nitrogen compounds found in refinery feeds and, thus, subject to considerable investigation into the kinetics of its hydrodenitrogenation (HDN). Although Jokuty and Gray1 recently questioned the use of quinoline as a model reactant for the HDN of real feeds, research continues, probably as much for basic knowledge of catalyst HDN properties, e.g., types of active sites, adsorption constants, as for its application to real feeds. The HDN of quinoline has been reviewed by Girgis and Gates.2 Figure 1 presents a simplified reaction network derived from the literature. Early studies assumed pseudo-first-order rates for all steps in the network. Later, it was recognized that N-containing intermediates in the reaction strongly adsorb on active sites, causing strong inhibition in reactivity of the various steps. The first significant investigation into the detailed kinetics of quinoline HDN was by Satterfield and coworkers.3,4 They assumed a single adsorption site and complete coverage of sites by adsorbed N-containing compounds. They also combined adsorbed species into several different groups. Other investigators assumed two different adsorption sites.5-9 More recent kinetic studies on the HDN of N-containing compounds have been carried out by Prins and co-workers.10-12 They deduced three different adsorption sites. In the above kinetic studies, supported NiMo catalysts were exclusively used. The object of the present investigation was to compare the detailed kinetics of the HDN reactions of quinoline with a CoMo and a NiMo catalyst under the same reaction conditions. Because a complete kinetic evaluation, employing the multiple adsorption sites proposed by Prins and co-workers, has not, to our knowledge, been reported, it was deemed important to carry out analyses of the entire reaction scheme to better compare catalysts. Extensive runs were made with quinoline and * To whom correspondence should be addressed.

decahydroquinoline at several feed concentrations and space times. The kinetics were modeled employing Langmuir-Hinshelwood equations with inhibition by N-containing species. Experimental Section The catalysts employed were Topsøe TK-554, which consisted of 4.1% CoO and 20.5% MoO3 supported on alumina (220 m2/g), and Topsøe TK-555, which consisted of 3.8% NiO and 24% MoO3 supported on alumina containing 2% phosphorus (160 m2/g). The 1.27-mm extrudates were crushed and sieved to 40- to 60-mesh particles. All runs were carried out in a fixed-bed reactor at 613 K and 3.5 MPa under vapor-phase conditions. Run conditions are given in Table 1. A 0.125-g sample of catalyst, mixed with 5 cm3 of glass beads, was presulfided with a 10% H2S/90% H2 mixture by volume under atmospheric pressure at 673 K for 2 h. The liquid feed consisted of 1/8-3/4 wt % quinoline or decahydroquinoline and 1.0 wt % dimethyl disulfide in n-heptane solvent. In some runs, 1/4 wt % orthopropylaniline or decahydroquinoline was added to 1/2 wt % quinoline. The hydrogen flow rate and liquid flow rate were varied proportionally so that a constant feed concentration was maintained at varying space time. The hydrogen partial pressure was approximately constant at 3.1 MPa, with the total pressure at 3.5 MPa. After the catalyst had been aged for 2 days under reaction conditions, its activity remained essentially constant over 300 h. Liquid samples taken at various space times were analyzed by gas chromatography (Hewlett-Packard, HP1, 30 m × 0.32 mm capillary column) using of a flame ionization detector and a temperature programming ramp of 10 K/min. The identities of individual products were determined by comparison with pure reference samples and GC/MS analysis (Topsøe Labs). Molar GC factors were determined using available samples. All species shown in Figure 1, including two isomers of propylcyclohexene (PCHE), were observed in the reaction product stream, except for o-propylcyclohexylamine (OPCHA), which was not detected. HDN conversion was calculated from the sum of the mole fractions of the non-N-containing compounds. Material balances

10.1021/ie020390t CCC: $25.00 © 2003 American Chemical Society Published on Web 01/28/2003

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Figure 1. Simplified reaction network for the hydrodenitrogenation of quinoline. Table 1. Run Conditionsa,b run

catalyst

A-1

CoMo

feedc 1/

1/ , 3/ % Q 2 4 % Q + 1/4% OPA 2 1/ % Q + 1/ % DHQ 2 4 1/ , 1/ , 1/ % Q 8 4 2 1/ % Q + 1/ % OPA 2 4 1/ % Q + 1/ % DHQ 2 4 1/ , 1/ , 3/ % DHQ 4 2 4 1/ , 1/ , 3/ % DHQ 4 2 4 1/ % DHQ + 1/ % OPA 2 4 4,

1/

A-2

NiMo

A-3 A-5

NiMo CoMo

a 613 K, 3.5 MPa, 3.1 MPa H , feed 0.17-0.51 mol/m3. b C (mol/ 2 o m3) ) 0.678 (% feed). c Percentages represent weight percentages of compound in heptane solvent with 1 wt % dimethyl disulfide.

were generally within 5%. Space time (τ) was defined as the weight of catalyst divided by the total gas flow (hydrogen plus vaporized liquid feed) at standard conditions (STP). The appropriate differential equations, representing various reaction networks, were solved for the parameters (rate constants and adsorption constants) using Scientist, version 2, by Micromath. This program also provides a simulation mode, with which the goodness of fit to experimental data can be visually checked by inputting and changing the values of the parameters before performing a least-squares analysis. The program provides a “goodness of fit” parameter called the model selection criterion (MSC) and 95% confidence intervals (CIs) on the parameter values, as well as complete statistics. The latter were used for F-tests to compare models. Results A. Quinoline HDN. Figure 1 shows the major reaction paths for the hydrodenitrogenation of quinoline (Q) according to the literature. The first part of the network is generally accepted; the specfic paths for the secondary products differ somewhat according to the investigator. Inspection of the data for the CoMo catalyst showed that Q was rapidly converted to 1,2,3,4-tetrahydroquinoline (THQ1), which was the major intermediate. Even at 40% HDN conversion, THQ1 remained the major compound. Thus, the conversion of THQ1 is a relatively slow step in the formation of non-N-containing products. Also, o-propylaniline (OPA) increased with space time, even when it was added to the Q feed, indicating that, initially, OPA forms faster than it reacts. Hence, this intermediate represents another slow step to non-N-containing products. For example, at a space time of 0.79 for 1/4% Q feed, HDN conversion was

52%, while the predominant unreacted species were THQ1 (20% mol/mol) and OPA (21%), showing that these intermediates reflect the slow steps in quinoline HDN. Figure 2a and b shows the fractional conversion of Q + THQ1 for runs A-1 (CoMo) and A-2 (NiMo) as a function of space time. This conversion is considered a more meaningful indication of of reactivity because of the very rapid conversion of Q to THQ1. The effect of feed concentration on reactivity indicates that the HDN reaction is strongly inhibited by reactant and/or products. The reactions involved in Figure 1 consist basically of hydrogenation (HYD) and C-N bond cleavage (CNH). To account for the inhibition, two separate sites were invoked: site A, a CNH site, and site B, a ring HYD site. In addition, separate adsorption constants for different adsorbed species were needed. As it is impractical to account for each species with a separate adsorption constant, several N-containing intermediate species were combined according to similarity in structure and basicity, viz.

site A (CNH): DA ) (1 + CoKA1Y1 + CoKA2Y2)n

(1)

site B (HYD): DB ) (1 + CoKBY3)n

(2)

where Co is the feed concentration, the Ki’s are adsorption constants, and the Yi’s are mole fractions of adsorbed species to be determined; the power n is also to be determined. Because the CNH site is acidic, Y1 includes strong basic species, whereas Y2 includes weaker basic species. For the HYD site, only one parameter was included, as it has been reported that all aromatic N-containing compounds have about the same adsorption constant on this site.13 The first approach was to analyze the decahydroquinoline runs to simplify the analysis and obtain estimates of the secondary parameters. Then, the quinoline runs were analyzed in small steps, starting with the primary reactions steps and then proceeding to include secondary steps in the reaction scheme, using the parameters from each step as initial estimates in the subsequent steps. B. Kinetics of HDN of Decahydroquinoline. Starting with decahydroquinoline (DHQ) as the feed, the major reaction products were PCHE, propylcyclohexane (PCH), and 5,6,7,8-tetrahydroquinoline (THQ5), with only small amounts of THQ1 ( values 5.68 1.21 most CIs > values 5.79 1.07 5.79 1.07 many CIs > values

f1 f2 f3 f4 f5 f6

run A-1 (CoMo): w/o k7 2/2 with k7 2/2 w/o k7 1/1 with k7 1/1 with k7 1/2 with k7 2/1

f7 f8 f9 f10 f11 f12

run A-2 (NiMo): Y1 ) D, Y2 ) B, Y3 ) Y4 ) B + D w/o k7 2/2 4.87 stdb with k7 2/2 4.78 1.09 w/o k7 1/1 4.95 1.07 many CIs > values with k7 1/1 4.95 1.0 many CIs > values w/o k7 1/2 4.85 1.03 w/o k7 2/1 5.00 1.14 most CIs > values

a D ) (1 + C K Y + C K Y )n, D ) (1 + C K Y )m, D ) 1 A o A1 1 o A2 2 B o B 3 C + CoKCY4 (for steps 8 and 9). b Model for comparison of F-ratios.

added two new rate constants, k6 and k7. After several simulation trials of the data for the CoMo catalyst (run A-1), it was found that an adequate fit to the data could k7 not be obtained unless a new, direct path THQ1 98 PCHE was included in the kinetic scheme (not evident in Figure 1). This is demonstrated by the statistical analyses. The MSC with path 7 included is much better than that obtained without path 7, and the F-test verifies that path 7 is real. On the other hand, the data for the NiMo catalyst failed to show a need for this step, the statistics being essentially the same with or without this step. Again, a square exponent in the inhibition term is clearly better. Step 4. Next, PCHE and PCH were separated to give the almost complete network, as detailed in Kinetic Scheme E. In accordance with Jian and Prins,13 a new site (site C) was used for double-bond HYD, i.e., PCHE f PCH. Therefore, the new parameter estimates needed were k8, k9, and KC. Statistical analyses demonstrated that use of the aromatic HYD site (site B) for this step gave less satisfactory results than use of a separate site C. No significant differencs in the data fits were obtained whether DC was to the first or second power; therefore, a first power was adopted for simplicity. Analyses showed at this point that the addition of Q and THQ5 to Y2 gave no improvement in the data fit, so such a step was consequently considered statistically unimportant. Step 5. In the above analyses, PB was neglected because of its very low concentration. To account for its formation, therefore, Kinetic Scheme F was adopted. Step 9 was added because, in the DHQ runs, some PB was observed to form while no OPA was present, indicating that PB most likely had formed from PCHE. In this case, the regression analysis was carried out with all previous parameters kept constant, except for the new parameters k9 and k10. Finally, all of the parameters were regressed. The statistical analyses reported in Table 2 show that, again, the denominator squared is superior. Also, F-tests again demonstrated that path 7 is valid for the CoMo catalyst but not for the NiMo catalyst, as found earlier (Kinetic Scheme D). The final parameter values for Kinetic Scheme F are given in Table 3. Figure 5 demonstrates data fits for the CoMo catalyst for a feed concentration of 1/4% Q (Q and PB omitted), and Figure 6a-c shows fits of individual species for all five data sets. Fits for THQ5 are essentially the same as in Figure 4. Figure 7 displays

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Kinetic Scheme C

the data fits for the NiMo catalyst for the run with added OPA. At this point, an exponent value of n ) 2 was better than n ) 1 for the CNH site, represented by DA, and for the HYD site, represented by DB. However, the possibility exists that the two exponents are not the same because the natures of the two sites are different. Therefore, we further investigated cases in which the two sites had different exponents. The results of the statistical analyses are given in Table 2. As can be seen, the cases with m ) 2 for DB are best, with m ) 1 giving very large CIs. However, either n ) 1 or n ) 2 with m ) 2 gives virtually the same results. Discussion Because of the large number of rate constants and adsorption constants involved in the reaction network of Figure 1, the kinetics of the entire network could not be uniquely solved by simultaneous solution of all

appropriate differential equations using the nonlinear regression analysis program. Thus, in fits of the data, different values of the parameters were obtained, depending on the initial values chosen, i.e., different local minima in least squares were obtained for different initial estimates. The problem then was to determine which set of parameters was correct, or at least reasonable. Hence, the approach was to start with smaller segments of the reaction network to establish some of the parameters before proceeding to the next step. A similar but more abbreviated method was adopted by Satterfield and Yang.4 Model Fitting. With a large reaction network containing many parameters, there is a danger of overparametization if sufficient data are not obtained. For Kinetic Scheme F (Table 3), there are a total of 17 parameters to be obtained, with 176 data points (40 individual runs with 8 species each), giving about 10 data points per parameter. For the first sequence of

Ind. Eng. Chem. Res., Vol. 42, No. 5, 2003 1017 Kinetic Scheme D

Kinetic Scheme B, there are about 9 data points per parameter. Hence, it seems that sufficient data should be available for the number of parameters to be determined. However, the space time range employed did not include low values, where THQ1 rapidly rises and then goes through a maximum (Figure 6a). Thus, accurate values of ko and koo could not be obtained because of the low values of Q in the experimental space time range. Nevertheless, this did not affect the determination of the other parameters, where appreciable changes in the concentrations of other species were obtained in the given space time range. The relatively large errors in some of the parameters in Table 3 are due to the low values or small changes with τ of the concentrations of the species associated with these parameters, especially the k values related to Q and THQ5, e.g., ko, koo, k2, k4, and k44. Thus, small errors in mole fraction values are magnified in the parameter values. However, large changes in these individual k’s had little effect on the other parameter values or on the data fits. In contrast, the k’s associated with relatively large concentrations or changes in

concentration of species such as THQ1 and DHQ exhibited reasonably small errors, e.g., k1, k5, k6, and k8. Kinetic analyses at several steps in the analysis failed to unequivocally distinguish statistically whether the inhibition terms for sites A and B should be to the first or second power. The models with inhibition terms to the first power gave significantly higher parameter CIs relative to the parameter values, sometimes as much as 7 times the parameter value. For example, for the case f4 (Table 2), the value of ko was 37 000 ( 154 000, and for the case of f9, ko was 16 000 ( 113 000. Also, the model with exponent 1 tended to blow up in some cases, giving very large values of ko, and did not always give the same values of the parameters on repeat trials. The significance of the exponent on the inhibition term is related to the mechanism of the surface reaction. Because reaction with hydrogen occurs in each case, for an exponent of 1, reaction of the adsorbed species on a given site either with molecular hydrogen on the same site or with adsorbed hydrogen on a different site could occur, whereas for an exponent of 2, only reaction of the

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Kinetic Scheme E

Table 3. Parameter Valuesa for Scheme F run A-1 CoMo

run A-2 NiMo

parameter

case f2

case f7

ko koo k1 k2 k3 k33 k4 k44 k5 k6 k7 k8 k9 k10 KA1 KA2 KB KC MSC

1810 ( 930 127 ( 65 1.31 ( 0.04 44 ( 19 0.6 ( 1.0 13 ( 4 65 ( 29 15 ( 7 5.1 ( 0.3 0.72 ( 0.14 1.32 ( 0.05 3.64 ( 0.15 0.24 ( 0.09 0.17 ( 0.12 3.0 ( 0.1 na 6.6 ( 1.7 0.26 ( 0.17 5.86

340 ( 130 23 ( 10 0.55 ( 0.05 23 ( 9 11.5 ( 2.6 23 ( 6 44 ( 19 13 ( 6 9.7 ( 0.5 0.74 ( 0.20 na 2.17 ( 0.12 0.38 ( 0.07 0.10 ( 0.15 16.4 ( 1.7 2.0 ( 0.3 9.6 ( 1.4 5.3 ( 2.6 4.88

a Units: k in m3/kg‚min, K in m3/mol. Plus/minus (() values indicate 95% CI.

adsorbed species on a given site with adsorbed hydrogen on the same type of site could occur. Hence, according to the results of Table 2, the CNH site (A) can have either exponents 1 or 2, whereas the aromatic HYD site (B) most likely requires an exponent of 2. Sites. Early on, it was found that one type of site was not adequate to fit the data. Because there are two basic types of reaction, viz., C-N bond cleavage and hydrogenation, it seemed logical to employ two different sites,

as discussed by Jian and Prins,13 viz., site A, a CNH site, and site B, an aromatic (and N-containing ring) HYD site. This model gave very good fits to the data up to the point when PCHE and PCH were considered separately in the kinetic analysis, at which point poorer fits were obtained using the aromatic HYD site (site B) for the reaction of PCHE to PCH (Kinetic Scheme E). Differences in the magnitudes of the K values also provide indirect evidence for the different sites. Thus, a third site, site C, for olefin hydrogenation was needed. Our three sites are similar to those reported by Jian and Prins11 for adsorption of N-containing compounds on NiMo catalysts. These authors later proposed an additional site for the direct denitrogenation of OPA to PB.13 Because of the low values of PB in our runs, with their attendant larger relative errors, such a separate site was not feasible, and this site was modeled with site A. Reaction Paths. No evidence was found for the presence of OPCHA in the reaction products of Q, although its presence was reported under some conditions by Jian and Prins.12 However, these authors reported virtually no OPCHA under conditions similar to ours, and its formation is expected to be very small.14 All aromatic hydrogenation reaction paths are reversible. Runs with DHQ as the feed showed that the path THQ5 T DHQ is reversible. Runs with Q and added DHQ were made to allow the kinetic evaluation of the reverse of reaction THQ1 T DHQ. A similar evaluation of the path Q T THQ5 could not be performed because THQ5 was not available for testing, and only the forward reaction was considered in the kinetics, be-

Ind. Eng. Chem. Res., Vol. 42, No. 5, 2003 1019 Kinetic Scheme F

directly as separate steps without reversibility, as the data did not warrant additional complications. Moreover, equilibrium for olefin hydrogenation under our conditions greatly favors the saturated compound.16 In a separate experiment, PB alone gave 8% conversion to PCH (5%) and PCHE (3%), independent of space time. In the presence of N-containing intermediates, these reactions would be negligible.17 A new path deduced from the kinetic analysis for the CoMo catalyst, defined by k7 and not part of the “normal” paths of Figure 1, represents an apparent “direct” reaction, i.e., THQ1 f PCHE. Gioia and Lee18 proposed such a path on the basis of their kinetic analysis of the HDN of quinoline. This reaction undoubtedly involves several elementary steps. If, according to Figure 1, the intermediate OPCHA is involved, then we might expect the following sequence: This Figure 5. Mole fractions vs space time for run A-1 (CoMo catalyst) for 1/4% Q feed. Solid curves are model fits for Kinetic Scheme F, case f2 (Table 2). Q and PB omitted.

cause, in any case, the values of THQ5 were quite low and the back reaction would be very small. Satterfield and Gultekin15 also assumed an irreversible step for this reaction. In all runs, the DHQ/THQ5 ratio increased gradually in the space time range for runs with Q as the feed, showing that equilibrium was not achieved. All CNH reactions were assumed to be irreversible. Olefin hydrogenation and dehydrogenation were treated

k7

very fast

THQ1 98 OPCHA 98 PCHE would involve a concerted reaction of HYD and CNH, leading to adsorbed OPCHA, followed by rapid surface reaction to PCHE and desorption. Thus, this path leading to PCHE is in competition with the normal paths, viz. k3

very fast

k5

THQ1 98 OPCHA 98 DHQ 98 PCHE.

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Figure 7. Mole fractions vs space time for run A-2 (NiMo catalyst) for Q + OPA feed. Curves are model fits for Kinetic Scheme F, case f7 (Table 2). Q and PB omitted.

Figure 6. Data fits for run A-1 (CoMo catalyst) according to Kinetic Scheme F, case f2: (a) Q and THQ1, (b) DHQ and OPA, and (c) PCHE and PCH.

Adsorption Constants. Although, in principle, all species in the HDN of quinoline could have different adsorption constants, it was necessary to group them to avoid overparametrization. Several authors have assumed the same adsorption constant for all N-containing intermediates.10,11,16,19-21 In other cases, certain compounds have been placed in separate groups.3,4,9,18 For the CNH site, we grouped species according to basicity into strongly adsorbed (group Y1) and weakly adsorbed (group Y2) species. For Y1 in the case of the CoMo catalyst, KA1 reflects mostly the adsorption constant for THQ1, as the ratio

of THQ1 to DHQ was on the order of 4-10, except when DHQ was added to the Q feed, when the ratio was 3. In fact, however, the adsorption constant for DHQ was essentially the same as that for THQ1, as shown by the results of analyses of Kinetic Scheme B. This is further confirmed by the nearly identical value of KA1(DHQ) ) 2.9 ( 0.2 derived from the DHQ run (Kinetic Scheme A) compared with its value of KA1(DHQ + THQ1) ) 3.0 ( 0.1 from the Q run (Kinetic Scheme F). For Y1 in the case of the NiMo catalyst, a different situation occurs. In this case, the adsorption constant KA1 represents the value for DHQ alone. For group Y2 (weakly adsorbed species on the CNH site), neither the scheme including Q nor that including THQ5 gave statistically better fits than the models without these species. For the CoMo catalyst, this meant that KA2 ) 0. It should be stressed that this does not mean that no adsorption of these species takes place, only that, under the run conditions, their inclusion in the inhibition term was statistically insignificant. The reason for the apparent lack of adsorption is probably their low concentrations (Q < 3%, THQ5 < 6%) and the small changes in their concentrations with space time. For the NiMo catalyst, KA2 represents the adsorption of THQ1 alone. OPA was not included in this group, as it was shown to have no effect when added to the DHQ feed (run A-5). Jian and Prins13 reported the adsorption constant of OPA to be some 4 times lower than those of Q-type compounds. The adsorption of ammonia (a product of HDN) was not considered, as it has been reported to be even weaker than the adsorption of OPA.3 For the HYD site (B), Jian and Prins13 reported that all of the N-containing compounds have about the same adsorption. Therefore, only one adsorption constant was considered. In this case, both DHQ and THQ1 were needed in the Y3 term. The addition of Q or THQ5 had no appreciable effect on the kinetics, which is not surprising in light of the low concentrations of these species with respect to the relatively larger concentrations of DHQ and THQ1. In the case of double-bond hydrogenation/dehydrogenation, a separate HYD site (site C) was needed, as application of the aromatic HYD site (site B) gave less satisfactory fits (Kinetic Scheme E). Further support for this approach comes from the different values of the adsorption constants KB and KC (Table 3), especially for the CoMo catalyst.

Ind. Eng. Chem. Res., Vol. 42, No. 5, 2003 1021

Comparison of Catalysts. An examination of Figure 2a and 2b clearly shows that, under comparable reaction conditions, the CoMo catalyst is more active than the NiMo catalyst for the conversion of Q + THQ1. This is partly due to the more rapid conversion of Q to THQ1 for the CoMo catalyst; thus, at the same space time, more THQ1 is available to react further. A significant difference in pathways emerges from the kinetic analyses. For the CoMo catalyst, an appreciable route for the conversion of THQ1 to PCHE was found (path 7), accounting for a relatively large fraction of THQ1 going to PCHE instead to DHQ, whereas this path was not evident for the NiMo catalyst. This alternate path might account for the greater HDN conversion for the CoMo catalyst. Differences in adsorption properties of the two catalysts are also evident. As seen in Table 3, the adsorption constants for DHQ and THQ1 for the CoMo catalyst are the same, whereas for the NiMo catalyst, the adsorption constant for DHQ is larger. Also, all adsorption constants are higher for NiMo than for CoMo. However, the values of KB are only marginally different (within the 95% CIs), whereas the values of KA are clearly different. This suggests that the promoter atom affects the adsorption properties of the CNH site (A) differently, but not the aromatic HYD site (B). This is in agreement with proposals that the CNH site is promoted by Ni, whereas the aromatic HYD site is associated with Mo via sulfur vacancies.7,13 The result that the CoMo catalyst gave a higher HDN conversion of quinoline than the NiMo catalyst is surprising in view of our earlier results with the same catalysts for indole HDN, in which NiMo was better,22 as well as the general acceptance, based on extensive testing with real feeds, that NiMo is superior for HDN, whereas CoMo is better for hydrodesulfurization.23 In fact, for the same catalysts used in our study, the NiMo catalyst was found to be a better HDN catalyst than the CoMo catalyst for real feeds under trickle-bed operation,24 contrary to our results with quinoline. It thus appears that the HDN of quinoline as a model reaction is a poor indicator of the HDN of real feeds, in agreement with Jokaty and Gray.1 Conclusions 1. A complete kinetic analysis of the individual paths in the HDN of quinoline required three separate types of active sites, viz., one for C-N bond scission, one for aromatic hydrogenation, and one for olefin hydrogenation. 2. Inhibition terms in Langmuir-Hinshelwood equations gave better fits to the data when squared. In general, adsorption constants of N-containing intermediates were higher for the NiMoP/Al2O3 catalyst than for the CoMo/Al2O3 catalyst. 3. An additional “direct” reaction path from 1,2,3,4tetrahydroquinoline to propylcyclohexene, not normally incorporated in the HDN network, was deduced for the CoMo catalyst but was absent for the NiMo catalyst. 4. Propylbenzene was a minor product and was formed mainly from the dehydrogenation of propylcyclohexene. 5. The CoMo/Al2O3 catalyst was more active than the NiMoP/Al2O3 catalyst for the HDN of quinoline under the reaction conditions employed. Symbols Co ) inlet feed concentration, mol/m3

CI ) confidence interval (95%) on a calculated parameter value D ) inhibition term in rate equations DHQ (D) ) decahydroquinoline F(5%) ) F-statistic at 5% for given degrees of freedom J ) PCHE + PCH k ) rate constant, m3/kg‚min K ) adsorption constant, m3/mol OPA (E) ) o-propylaniline OPCHA ) o-propylcyclohexylamine PB (H) ) propylbenzene PCH (G) ) propylcyclohexane PCHE (F) ) propylcyclohexene Q (A) ) quinoline THQ1 (B) ) 1,2,3,4-tetrahydroquinoline THQ5 (C) ) 5,6,7,8-tetrahydroquinoline V ) OPA + PCHE + PCH Z ) Q + THQ1 τ ) space time, kg‚min/m3

Acknowledgment Support of this research by Haldor Topsøe A/S is gratefully acknowledged. We also thank Per Zeuthen of Haldor Topsøe A/S for the GC/MS analyses. Literature Cited (1) Jokuty, P. L.; Gray, M. R. Nitrogen Bases Resistant to Hydrodenitrogenation: Evidence against Quinoline as a Model Compound. Ind. Eng. Chem. Res. 1992, 31, 1445. (2) Girgis, M. J.; Gates, B. C. Reactivities, Reaction Networks, and Kinetics in High-Pressure Catalytic Hydroprocessing. Ind. Eng. Chem. Res. 1991, 30, 2021. (3) Satterfield, C. N.; Cocchetto, J. F. Reaction Network and Kinetics of the Vapor-Phase Catalytic Hydrodenitrogenation of Quinoline. Ind. Eng. Chem. Process Des. Dev. 1981, 20, 53. (4) Satterfield, C. N.; Yang, S. H. Catalytic Hydrodenitrogenation of Quinoline in a Trickle-Bed Reactor. Comparison with Vapor Phase Reaction. Ind. Eng. Chem. Process Des. Dev. 1984, 23, 11. (5) Shih, S. S.; Katzer, J. R.; Kwart, H.; Stiles, A. B. Quinoline Hydrodenitrogenation: Reaction Network and Kinetics. Am. Chem. Soc. Div. Pet. Chem. Prepr. 1977, 22, 919. (6) Bhinde, M. V.; Shih, S.; Zawadski, R.; Katzer, J. R.; Kwart, H. Hydrodenitrogenation over Molybdenum-Containing Catalysts. In Proceedings of the Third International Conference on the Chemistry and Uses of Molybdenum; Barry, H. F., Mitchell, P. C. H., Eds.; Climax Molybdenum Co.: Ann Arbor, MI, 1979; p 184. (7) Yang, S.-H.; Satterfield, C. N. Some Effects of Sulfiding of a NiMo/Al2O3 Catalyst on Its Activity for Hydrogenation of Quinoline. J. Catal. 1983, 31, 168. (8) Vivier, L.; Kasztelan, S.; Perot, G. Kinetic Study of the Decomposition of 2,6-Dimethylaniline in the Presence of 1,2,3,4Tetrahydroquinoline over a Sulfided NiMo-Al2O3 Catalyst. I. Effect of Partial Pressure of Nitrogen Compounds. Bull. Soc. Chim. Belg. 1991, 100, 801. (9) Vivier, L.; D’Araujo, P.; Kasztelan, S.; Perot, G. Kinetic Study of the Decomposition of 2,6-Dimethylaniline in the Presence of 1,2,3,4-Tetrahydroquinoline over a Sulfided NiMo-Al2O3. II. Effect of H2S. Bull. Soc. Chim. Belg. 1991, 100, 807. (10) Rico Cerda, J. L.; Prins, R. Kinetic Study of the Effect of Phosphorus in the HDN of 5-Tetrahydroquinoline over Ni-MoS/ γ-Al2O3 Catalysts. Bull. Soc. Chim. Belg. 1991, 100, 815. (11) Jian, M.; Prins, R. Kinetics of the hydrodenitrogenation of decahydroquinoline over NiMo(P)/Al2O3 catalysts. Ind. Eng. Chem. Res. 1998, 37, 834. (12) Jian, M.; Prins, R., J. Mechanism of the Hydrodenitrogenation of Quinoline over NiMo(P) Catalysts. J. Catal. 1998, 179, 18. (13) Jian, M.; Prins, R. Determination of the nature of distinct catalytic sites in hydrogenation by competitive adsorption. Catal. Lett. 1998, 50, 9. (14) Cocchetto, J. F.; Satterfield, C. N. Chemical Equilibria among Quinoline and Its Reaction Products in Hydrodenitrogenation. Ind. Eng. Chem. Process Des. Dev. 1981, 20, 49.

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(15) Satterfield, C. N.; Gu¨ltekin, S. Effect of Hydrogen Sulfide on the Catalytic Hydrodenitrogenation of Quinoline. Ind. Eng. Chem. Process Des. Dev. 1981, 20, 62. (16) Satterfield, C. N.; Modell, M.; Hites, R. A.; Declerck, C. J. Intermediate Reactions in the Catalytic Hydrodenitrogenation of Quinoline. Ind. Eng. Chem. Process Des. Dev. 1978, 17, 141. (17) Jian, M.; Kapteijn, F.; Prins, R. Kinetics of the Hydrodenitrogenation of ortho-Propylaniline over NiMo(P)/Al2O3 Catalysts. J. Catal. 1997, 168, 491. (18) Gioia, F.; Lee, V. Effect of Hydrogen Pressure on Catalytic Hydrodenitrogenation of Quinoline. Ind. Eng. Chem. Process Des. Dev. 1986, 25, 918. (19) Miller, J. T.; Hineman, M. F. Non-First-Order Hydrodenitrogenation Kinetics of Quinoline. J. Catal. 1984, 85, 117. (20) Gu¨ltekin, S.; Khaleeq, M.; Al-Sajeh, M. A. Combined Effects of Hydrogen Sulfide, Water, and Ammonia on the LiquidPhase Hydrodenitrogenation of Quinoline. Ind. Eng. Chem. Res. 1989, 28, 729.

(21) Sundaram, K. M.; Katzer, J. R.; Bischoff, K. B. Modeling of Hydroprocessing Reactions. Chem. Eng. Commun. 1988, 71, 53. (22) Kim, S. C.; Massoth, F. E. Kinetics of the Hydrodenitrogenation of Indole. Ind. Eng. Chem. Res. 2000, 39, 1705. (23) Topsøe, H.; Clausen, B. S.; Massoth, F. E. Hydrotreating Catalysis. In CatalysissScience and Technology; Anderson, J. R., Boudart, M., Eds.; Springer-Verlag: New York, 1996; Vol. 11, p 1. (24) Zeuthen, P. Haldor Topsøe A/S, Lyngby, Denmark. Private communication.

Received for review May 28, 2002 Revised manuscript received December 3, 2002 Accepted December 4, 2002 IE020390T