Hydrogenation and hydrocracking of a model light cycle oil feed. 2. Properties of a sulfided nickel-molybdenum hydrocracking catalyst

1592 Ind. Eng. Chem. Res. 1993,32, 1592-1602

Hydrogenation and Hydrocracking of a Model Light Cycle Oil Feed. 2. Properties of a Sulfided NiMo Hydrocracking Catalyst

Michel Bouchy,+ Sylvie Peureux-Denys? Pierre Dufresne? and Slavik Kasztelan' Institut Franqais du Pktrole, 1 et 4 Avenue de Bois-Prkau, BP 311, 92506 Rueil-Malmaison Cedex, France

A synthetic model light cycle oil feed containing 40 5% w/w 1-methylnaphthalene, dimethyl disulfide, and n-butylamine in n-heptane has been treated under hydrogen on a sulfided NiMoP/zeolite HY-Al203 catalyst. Reference conditions were a hydrogen pressure of 28 atm, a temperature of 400 "C, and a liquid hourly space velocity of 1 m3 h-' m3cat. The diaromatic undergoes a fast hydrogenation and is in quasi-equilibrium with the corresponding methyltetralins. The group of diaromatics and alkyltetralins evolves through isomerization, methylation, and demethylation. It is converted into alkylindans and alkylbenzenes, the latter evolving towards BTX (benzene, toluene, and xylene) compounds and light paraffins. The numerous compounds in the effluents can be lumped into the three major groups diaromatic-alkyltetralins, alkylindans, and alkylbenzenes, which allows us to propose a simple kinetic scheme for the whole reaction. The inhibition of the reactions by NH3, HZS, and the aromatics has also been investigated, and i t has been found that the aromatics have the strongest inhibiting effect.

Introduction

The hydrotreating of light cycle oil (LCO), a by-product of fluid catalytic cracking, is a possible way to improve its quality by performing desulfurization, denitrogenation, and hydrogenation so that it can be incorporated into the gas-oil pool. An increase in the cetane number is however needed for the hydrotreated LCO. This could be obtained by conversion of the polyaromatics into alkylbenzenes, Le., by partial hydrogenation followed by opening of the saturated rings.

Little is known about the kinetics of simultaneous hydrogenation and conversion of polyaromatics in the presence of sulfur and nitrogen. Such conversions have been assessed using various heterogeneous catalysts for the above process or with the aim of converting polyar- omatic compounds produced in coal pyrolysis: sulfide/ silica-alumina (Flinn et al., 1960; Qader and Hill, 1972), Co-Mo suKde/alumina (Huang et al., 19771, Ni-W sulfide/ zeolite (Haynes et al., 1983; Wuu and Hatcher, 1983), Ni- Mo sulfide/zeolite (Fischer e t al., 19891, Cr-Mo-Ba/AlzO3 (Perrot and al., 1988), and alkali-Fe (Sawyer and Hudson, 1989).

In the first part of this work (Bouchy et al., 1992) it has been shown that a conventional NiMoP/alumina hydrotreating catalyst was not able to perform hydrocracking of the saturated rings to a great extent. The aim of this present work is to improve our knowledge of the reactions of hydrogenation and hydroconversion of a model diaromatic compound on a conventional sulfided NiMo hydrocracking catalyst. We analyze in the following the effect of the reaction conditions on the product distribution including the inhibiting effect of NH3 and H2S and discuss the kinetics of the reaction by taking into account the results on hydrogenation and primary steps of hydrocracking obtained in the first part of this work.

* To whom correspondence may be addressed. E-mail:

t On leave of absence from URA 328 du CNRS, ENSIC, 1 rue

t Present address: Institut de Recherche sur la Catalyse 2,

8 Present address: Eurecat S.A., BP 45, 07800 La Voulte/

kasztelana cl.ifp.fr.

Grandville, BP 451, 54001 Nancy Cedex, France.

Avenue A. Einstein, Villeurbanne Cedex, France.

Rhhe, France.

Experimental Section

The catalyst used was a Ni-Mo-P oxide on y-alumina and zeolite HY in the form of extrudates containing 16% zeolite, 3% NiO, 13% Moo3, and 5% PZOS w/w. The experimental setup, catalyst sulfurization conditions, and reactants were similar to those described in detail in the previous part for the NiMoP/alumina hydrotreating catalyst (Bouchy et al., 1992). Then only the experimental conditions specific to this work will be addressed in the following.

The reference operating conditions for the catalytic tests were reaction temperature, 400 "C; total pressure, 40 atm;

aromatic, 8.3 mol/mol (Hdfeed, 450 v/v). In the following, the "contact time" (l/LHSV) will be

used instead of the LHSV and expressed in hours. The liquid feed composition was (percentage in weight

and partial pressures in the reactor) 40% 1-methylnaphthalene (3.5 atm), 57.75% n-heptane (7.2 atm), 2% dimethyl disulfide (DMDS) (i.e., 0.28 atm of HzS), and 0.25% n-butylamine (NBA) (i.e., 0.043 atm of "3).

The additives DMDS and NBA decompose quickly to give H2S and NH3 thus allowing us to simulate the S and N content of a standard real feed (i.e., 1.4% S and 480 ppm N w/w). The hydrogen pressure was then 29 atm a t the entrance to the reactor and about 28 atm at the exit after partial hydrogenation of the diaromatic.

A stabilization time of several hours was allowed before each experiment, and all measurements were then done at the steady state. In order to check the catalyst stability, a reference experiment was carried out a t three different times during this study and no significant variations of the catalyst activity were found. There was therefore no aging of the catalyst, and poisoning by ammonia was a reversible process.

In order to check the material balance, the flow of liquid feed was verified and the integrated mass of this feed was compared with the mass of liquid effluents. A recovery of about 98 wt % of the material was observed. Some loss can be attributed to gaseous light alkanes.

Analysis of the liquid effluents was performed using gas-phase chromatography on a Varian chromatograph Vista-6000. Two columns have been used: (1) a CPSIL5 column, length 50 m, diameter 0.42 mm, film thickness

liquid hourly space velocity (LHSV), 1 m3 h-' m-3 cat; Hd

0888-588519312632-1592$04.00/0 0 1993 American Chemical Society

Ind. Eng. Chem. Res., Vol. 32, No. 8, 1993 1593

4.94 5.32 5.64 6.80 7.43

10.17 10.98 12.06 13.89 14.09 14.40 14.87 16.15 16.70 17.06 18.04 18.19 18.99 19.64 19.95 20.09 20.26 22.13 24.29 24.85 29.02 44.08 45.54 45.72 49.31 61.36 61.80 66.84 73.17 77.42 78.55 81.07 81.85 85.21

85.49 87.65 87.97

88.28 88.69 90.33 90.43

91.84 92.84 93.30 93.58 94.89

95.90

96.88

97.46 97.68 98.14 98.30 98.74

propane isobutane n-butane isopentane n-pentane 2-methylpentane 3-methylpentane n-hexane 2,2-dimethylpentane methylcyclopentane 2,4-dimethylpentane 2,2,3-trimethylbutane benzene 3,3-dimethylpentane cyclohexane 2-methylhexane 2,3-dimethylpentane 3-methylhexane cis-l,3-dimethylcyclopentane ?-dimethylcyclopentane trans-l,3-dimethylcyclopentane tram-l,2-dimethylcyclopentane n-heptane methylcyclohexane ethylcyclopentane toluene ethylbenzene p - x y 1 en e m-xylene o-xylene alkylbenzene alkylbenzene alkylbenzene indan n-butylbenzene tram-decalin 2-methyliidan l-n&ylindan

dimethylindan cis-decalin methyldecalin alkylbenzene methyldecalin 3-methylbutylbenzene dimethyliidan 5-methylindan l,3-dimethylindan 1-methyldecalin 4-methylindan methylbutylbenzene tetralin n-pentylbenzene alkylbenzene 1-methyldecalin naphthalene 1-methyldecalin dimethyliidan 1-methyldecalin dimethylindan l,?-dimethylindan dimethylindan dimethylindan l,?-dimethylindan

nzene

3 4 4 5 5 6 6 6 7 6 7 7 6 7 6 7 7 7 7 7 7 7 7 7 8 7 8 8 8 8 9 9 9 9

10 10 10 10 11 11 10 11 11 11 11 11 10 11 11 10 11 10 11 11 11 10 11 11 11 11 11 11 11 11

44 58 58 72 72 86 86 86

100 84

100 100 78

100 84

100 100 100 96 96 96 96

100 98 98 92

106 106 106 106 120 120 120 118 134 138 132 132 148 146 138 150 148 152 148 146 132 146 152 132 148 132 148 148 152 128 152 146 152 146 146 146 146 146

Table I. Chromatographic Analysis on a PONA Column of the Effluent from the Hydrocracking of the Model LCO Feed (Contact Time 0.6 h; Otherwise Reference Conditions)

retention no. of molecular retention no. of molecular time C ma88 % time C mass % (rnin) products atoms (g/mol) w/w (min) products a tom (g/mol) w/w

0.054 100.92 2-methyltetralin (2MT) 11 146 2.028 0.096 0.239 0.104 0.103 0.024 0.021 0.030 0.003 0.131 0.069 0.0oO 0.194 0.0oO 0.029 0.769 0.121 0.846 0.055 0.041 0.070 0.037

61.367 0.170 0.011 0.553 0.083 0.117 0.061 0.078 0.056 0.026 0.041 0.139 0.056 0.050 0.165 0.244 0.135

0.030 0.093 0.198

0.119 0.089 0.414 0.166

0.394 0.448 1.764 2.257 0.120

1.164

0.391

0.549 0.640 0.860 0.340 0.481

101.99 103.11 103.29

104.86

105.27 105.72 106.52

106.92 107.26 107.49 108.54 108.90

109.79

110.39 110.70 111.37 112.94 113.26 113.61 115.21 115.46 118.66 120.06 120.35 121.02 121.20 122.39 122.71 124.18 125.46 129.99 131.29 131.80 132.26 133.52 133.86 137.04 137.72 145.04 145.18 145.51 147.03 147.44 149.15 22.13 85.21 85.21

108.90 108.90 110.70 110.70 112.94 112.94 133.86 133.86 137.04 137.04 150.00

1-methyltetralin (IMT) dimeth ylindan dimethylindan alkylbenzene dmethylindan alkylbenzene dimethylindan alkylbenzene methylpentylbenzene alkylbenzene 6-methyltetralin (6MT) alkylidan alkylbenzene alkylindan alkylbenzene alkylindan 5-methyltetralin (5MT) 2-methylnaphthalene (2MN) al ky 1 in d an alkylindan I -methylnaphthalene (1MN) dimethyltetralin dimethyltetralin dimethyltetralin dimethyltetralin dimethyltetralin ethylnaphthalene dimethyltetralii dimethyltetralin dimethylnaphthalene dimethylnaphthalene dimethylnaphthalene dimethylnaphthalene dimethylnaphthalene dimethylnaphthalene trimethylnaphthalene trimethylnaphthalene trimethylnaphthalene trimethylnaphthalene trimethylnaphthalene trimethylnaphthalene methylbiphenyl methylbiphenyl dimethylbiphenyl dimethylbiphenyl dimethylbiphenyl dimethylbiphenyl dimethylbiphenyl phenanthrene various of group B

various of groups B and I

various of group I

various of groups I and NT

various of group N!C

various of groups NT and BP

various of group BP

11 11 11 12 11 12 11 12 12 12 11 12 12 12 12 12 11 11 12 12 11 12 12 12 12 12 12 12 12 12 12 12 12 12 12 13 13 13 13 13 13 13 13 14 14 14 14 14 14 9-11

11-12

12

12

12-13

13

13-14

146 146 146 162 146 162 146 162 162 162 146 160 162 160 162 160 146 142 160 160 142 160 160 160 160 160 156 160 160 156 156 156 156 156 156 170 170 170 170 170 170 168 168 182 182 182 182 182 178 120-148

148-162

160

156-160

156-174

168-174

168-182

0.839 0.058 0.092

0.066

0.140 0.206 0.145

4.200 0.057 0.062 0.030 0.045

7.920

0.110 0.094 2.774 0.344 0.070 0.071 0.086 0.074 0.020 0.222 0.106 0.272 0.279 0.557 0.283 0.205 0.085 0.039 0.041 0.036 0.024 0.014 0.015 0.048 0.022 0.034 0.041 0.043 0.023 0.000 0.011 0.497

0.309

0.015

0.018

0.252

0.011

0.022

0.4 pm, using a programmed temperature (20 "C for 5 min followed by an increase up to 280 "C a t a rate of 5 OC/min), and a He flow of 1 cm3/min; (2) a PONA column from Hewlett-Packard, length 50 m, diameter 0.2 mm, film thickness 0.5 pm, using a programmed temperature (35 OC for 10 min, an increase up to 114 "C at a rate of 1 OC/min, and an increase up to 280 "C at a rate of 1.7 OC/ rnin), and a He flow of 0.93 cmg/min.

Detection was achieved by a flame ionization detector.

The identification of the products was carried out using chromatography coupled with mass spectrometry.

Reaction products

A typical chromatographic analysis carried out on a PONA column is given in Table I. Apart from the two reactante n-heptane and 1-methylnaphthalene, 108 products peaks are listed. Identification has been carried out

1594 Ind. Eng. Chem. Res., Vol. 32, No. 8, 1993

using mass spectrometry coupled with chromatography. About half of the peaks listed in Table I have been clearly identified. The other half consists of various isomers of known family and carbon number but where alkyl substitution groups are not actually known. Partial identification of these peaks has been eased by the fact that there is no redundancy in the molar masses in the various alkyl-substituted benzene, cyclohexane, naphthalene, tetralin/indan, and decalin possessing 6-13 C atoms. Note that the PONA column does not separate two major products: 2-methylnaphthalene and 5-methyltetralin. However, these products are readily separated on the SIL5 column.

Owing to the presence in the effluent of many products in very low quantities, the identification is not complete. Thus, a proportion of about 30% in weight of the actual products of 1-methylnaphthalene hydrocracking was not identified under the reference conditions. This, together with the numerous number of products, has led us to carry out a lumping of the products and an estimation of the unidentified minor chromatographic peaks.

From the present study and preceding results on a NiMoP/Alumina catalyst of low cracking activity, the lumping has been made within five groups: Group A, low carbon number alkanes (n-heptane and isomers and alkanes of lower mass); group B, alkylbenzenes and alkylcyclohexanes (benzene and cyclohexane included); group I, alkylindans (indan included); group NT, alkylnaphthalenes and alkyltetralins (naphthalene and tetralin included); group BP, alkylbiphenyls.

Group A was considered to consist mainly of products of n-heptane hydrocracking or the loss of substituents by compounds of the other groups (methane, ethane, and probably part of the propane were in the gaseous effluents which were not titrated).

In group B, the main products are alkylbenzenes. The corresponding alkylcyclohexane derivatives, in smaller quantity, are also included to account for the formation of their parent products.

Group I contains all the alkylindans. Hexahydrogenated alkylindans (or hydrindanes) could be formed but they were not detected.

Group NT encompasses alkylnaphthalenes and their tetrahydrogenated derivatives alkyltetralins. As shown below, there is indeed a very fast hydrogenation of the diaromatics into alkyltetralins up to the thermodynamic equilibrium. Further hydrogenation leading to the decahydrogenated derivatives (alkyldecalins) is by contrast slow and of small extent.

Alkylbiphenyls (group BP) constitute only a minor group. Condensed aromatics of high carbon number are presumably formed in small quantitites, but they were not detected under the operating conditions.

The unidentified products present in small quantities are likely to be the numerous isomers of the identified products, this being due to the presence of one or more substituting methyl groups. In order to account for these, an assumption has been made in order to sort them out in one of the lumping groups. An interval of retention times was allotted to each group, limited by the shortest and the longest retention time within the identified group members. Any unidentified peak within this interval was then included in this group. In the case of two overlapping groups, the peak areas were equally shared between the two groups. In the case of peaks within a gap between two groups, they were also equally shared between the two adjacent groups. According to these rules, seven retention time intervals were then defined as shown in the last section of Table I in order to sort out the unknown compounds present in small quantity.

E z w -1 a t I1 a a 3 > I

t 5 $ O

2 b

$ -1

E 3

a 3 E U

2 w

1.4 1.5 1 OOOn (1 /K)

1.6

Figure 1. van’t Hoff plot of molar ratios T/N of concentrations of methyltetralins to parent methylnaphthalenes (reference conditions). (0, full line) Hydrogenation of 1-methylnaphthalene; (+, broken line) hydrogenation of 2-methylnaphthalene.

Hydrogenation of the Diaromatics Hydrogenation Equilibrium of Methylnaphtha-

lenes. Two possible methyltetralins are formed from each of the two methylnaphthalenes, corresponding to the hydrogenation of one of the two aromatic rings. The quantity of the methyltetralin corresponding to the hydrogenation of the substituted ring (5MT or 6MT) is found to be about 2.5 times as much as the one corresponding to the hydrogenation of the nonsubstituted ring (1MT or 2MT), in qualitative agreement with our previous study (Bouchy et al., 1992). As the relative proportion between the two methyltetralins arising from a parent methylnaphthalene appears to vary only slightly with temperature (and is, on principle, independent of the hydrogen pressure), each hydrogenation equilibrium has then been followed by considering the total amount of corresponding methyltetralins.

We have shown in our previous study that, using a hydrotreating catalyst of similar hydrogenation function as the present one (NiMoPly-AlnOa), a very fast first hydrogenation of the first ring of the 1-methylnaphthalene into 1- and 5-methyltetralins was taking place and was limited by the thermodynamic equilibrium. By contrast, the hydrogenation of the second ring, leading to the decahydrogenated derivative 1-methyldecalin, was found to be slow and of small extent.

Equilibrium conditions were also observed in the present study in the case of 1-methylnaphthalene hydrogenation and in the case of the hydrogenation of L-methylnaphthalene (present in the medium as the main product of conversion of 1-methylnaphthalene, in agreement with the previous study). This is indeed verified by the variation of the molar ratio T/N of methyltetralins to the parent methylnaphthalenes determined for a contact time of 1 h.

The variations of ln(T/N) vs 1 /T (K-I) a t constant hydrogen pressure are straight lines (cf. Figure 1) from which the values of the enthalpies of the hydrogenation reaction A H O T N can be found; these are in agreement with values found in the previous study using a hydrotreating catalyst (cf. Table 11). Note that in the case of 2-methylnaphthalene hydrogenation on this catalyst, the data are not accurate because of a small amount present a t low temperature.


b 0.4-

I

I

2 0.2-

0.0 1000.0 2c [HYDROGEN PRESSURE (atrn)12

Figure 2. Variations of ratios T/N of concentrations of methylte- tralina to parent methylnaphthalenes vs hydrogen preseure (reference conditions). (0, full line) Hydrogenation of l-methylnaphthalene; (+, broken line) hydrogenation of 2-methylnaphthalene.

Table 11. Thermodynamic Data for the First Hydrogenation of Methylnaphthalenes (1MN and 2MN) Determined from Experimental Molar Ratios T/N of Methyltetralins (lMT, 5MT, 2MT, and 6MT) to Parent Methylnaphthalenes.

).O .,.- ,

0.0 0.5 1 .o CONTACT TIME (h)

A H o ~ (kcal) Km(400 "C) (atm-2) hydro- hydro- hydro- hydro-

treating cracking treating cracking T/N catalyst catalyst catalyst catalyst

(1MT + 5MT)/lMN -29 -31 9.4 X lo-" 6.8 X lo-" (2MT+ 6MT)/2MN (-33) -29.6 7.8 X lo-" 7.3 X lo-"

a Hydrotreating catalyst, Bouchy et al. (1992); hydrocracking catalyst, this work. morn, standard enthalpy of hydrogenation; KTN, thermodynamic equilibrium constant.

The T/N ratios also vary linearly with PH: at constant temperature (cf. Figure 2). The value of the equilibrium constant KTN (at the experimental temperature of 400 "C) is determined from the slope of these straight lines (at the experimental temperature of 400 "C). The results and a comparison with the data from our previous study are given in Table 11, where only a small discrepancy appears in the case of the hydrogenation of l-methylnaphthalene (cf. Table 11). A smaller conversion in the case of l-methylnaphthalene could be attributed to a lower hydrogen pressure in the present experiments. However this has to be ruled out in view of the good agreement in the case of 2-methylnaphthalene.

On the whole, a satisfactory agreement is found between experiments using both catalysts and shows that the thermodynamic equilibrium is therefore attained under the reference conditions (especially a t a temperature of 400 "C and contact time of 1 h).

Evolution of the Hydrogenation withcontact Time. According to our previous study (Bouchy et al., 1992), a very fast hydrogenation of l-methylnaphthalene takes place under the reference conditions and the system is considered to be near thermodynamic equilibrium at 400 "C after an hypothetical contact time of about 1 min.

A similar kinetic scheme is expected in the case of the present catalyst, thus leading to a practically constant T/N ratio of methyltetralins to parent methylnaphthalene concentrations throughout the course of reaction over 1 h at 400 "C. However, as shown in Figure 3, a decrease

5

Figure 3. Evolution with contact time of ratioT/N of methyltetralins to parent methylnaphthalene concentrations (reference conditions). (0) Hydrogenation of l-methylnaphthalene; (+) hydrogenation of 2-methylnaphthalene.

of this ratio is observed in the case of both methylnaphthalenes. The T/N ratio appears to be nearly twice as large as the expected value at short contact time, and the agreement found between this study and the previous one on the hydrogenation catalyst is only observed at a contact time of about 0.5 h.

The proportion of methyltetralins reached at short contact time is then apparently higher than the one expected from thermodynamic equilibrium. This is against thermodynamic laws and is presumably due to an artifact. The excess of hydrogenation could be attributed to experimental error in the measurement or setting of the temperature or of the hydrogen pressure. However, the ratios measured at a contact time of about 0.12 h would be consistant with a temperature of 380 "C instead of 400 "C or a hydrogen p r e s s w f 40 atm instead of 28 atm, and such differences are outside experimental error. The temperature, in particular, was checked along the reactor and inside the thermometric well and variations of f 2 "C were found.

In conclusion, the ratio of methyltetralins to methylnaphthalene concentrations is close to the expected value at the thermodynamic equilibrium for most of the course of the reaction. This hydrogenation is completed very quickly (for a contact time of less than 0.12 h) in agreement with the results obtained in the preceding study. For simplicity's sake, we will assume in the following a perfect and immediate thermodynamic equilibrium for the hydrogenation of the first ring. Thus, the methyltetralins and their parent methylnaphthalenes will be indistin- guishable in the kinetic model.

Hydrogenation of Alkylnaphthalenes. The assumption of a quasi-equilibrium for the hydrogenation of the first ring can also be made in the case of the various alkylnaphthalenes produced in the course of the reaction. It is indeed a general rule that the rate of hydrogenation increases when the substitution of the aromatic increases (Dufresne et al., 1987). The theoretical T/N ratio asso- ciated with the various dimethylnaphthalenes has been estimated using the method of Benson (Benson, 1976) and the system tetralin-naphthalene as a reference (Frye and Weitkamp, 1969). Such a calculation has been described and carried out in our previous study with a satisfactory


Table 111. Theoretical Thermodynamic Data for Hydrogenation of Dimethylnaphthalenes (Except 1,8-Dimethylnaphthalene). compound Km(400 "C) (atm-2) M o m (kcal/mol) T/N % N 12N-12T 12N-56T 13N-13T 13N-57T 14N-14T 14N-58T 15N-15T 16N-16T 16N-25T 17N-17T 17N-28T 18N-18T 23N-23T 23N-67T 26T-26N 27T-27N

0.25 X lo-' 8.5 X lo-' 0.16 X lo-' 8.5 X lo-' 0.16 X lo-' 8.5 X lo-' 0.82 X lo-' 0.82 X lo-' 0.16 X lo-' 0.82 X lo-' 0.16 X lo-'

0.49 X lo-' 8.5 X lo-' 3.2 X lo-' 3.2 X lo-'

-23.7 -32 -23.5 -32 -23.5 -32 -27.5 -27.5 -28 -27.5 -28

-24.2 -32. -28. -28.

0.020 0.666 0.012 0.666 0.012 0.666 0.064 0.064 0.127 0.064 0.127

0.038 0.666 0.253 0.253

6.3 6.3

18.1 18.1 9.0 9.0 9.0

18.1 18.1 18.1 18.1 0 3.2 3.2 9.0 9.0

a Compounds: xyN-z'y'T is short for ry-dimethylnaphthalene- r' y'-dimethyltetralin. Km, thermodynamic equilibrium constant; pHom, standard enthalpy of hydrogenation; T/N, molar ratio of alkyltetralin to parent alkylnaphthalene (under reference conditions T = 400 "C, P H ~ = 28 atm); % N, molar percentage of dimethylnaphthalene in a mixture of the diaromatics at thermodynamic equilibrium.

agreement in the case of 1-methylnaphthalene. There are 10 isomers of dimethylnaphthalene and 16 isomers of dimethyltetralins, and the corresponding theoretical T /N ratio can take several values. These are reported in Table I11 (except for 1,8-dimethylnaphthalene, where a strong steric hindrance takes place). An average value of about 0.4 is found under the reference conditions. This averaging has been carried out assuming a distribution of the isomers in thermodynamic equilibrium (Alberty and Bloomstein, 1985). In agreement with Dufresne et al., the extent of hydrogenation at thermodynamic equilibrium decreases when the substitution of the aromatic increases (T/N of 0.8 for methylnaphthalenes and 1.4 for naphthalene). The average value of the hydrogenation enthalpy is found to be about -28 kcal/mol.

A similar amount of naphthalene and of dimethylnaphthalenes is produced in the course of the reaction (cf. below). Thus, when all alkylnaphthalenes and alkyltetralins are lumped together in the unique NT group, with a major participation of methylnaphthalenes, the kinetic model developed later will assume average thermodynamic properties based mainly on the hydrogenation of the methylnaphthalenes.

Hydrocracking of 1-Methylnaphthalene

Introduction. The hydrocracking of an alkane such as n-heptane leads mainly to isomerization products (methylhexanes) and cracking into alkanes of lower molecular mass (Quesada-Perez, 1989; Baltanas e t al., 1983; Vasquez et al. 1987). Under the reference experimental conditions, the formation of the main products of isomerization (2- and 3-methylhexane) and cracking represents a conversion of n-heptane of about 4.6%, which is small compared with the conversion of the diaromatic and/or monoaromatics (about 33 % 1.

Runs carried out on an inert solid (carborundum) show that thermal hydrocracking of the diaromatic is negligible up to 440 "C. Thermal studies on tetralin (Bastick et al., 1988) show also that this kind of compound is stable in this temperature range. Therefore, we will then consider in the present study that the catalytic hydrocracking of 1-methylnaphthalene is the main reaction of the feed.

Overall Evolution of the Hydrocracking with the Main Parameters. The influence of the contact time, the temperature, and the pressure has been studied by varying each parameter around the value set for the reference conditions. The NT group, originally l-methylnaphthalene on its own, is considered as the reactant, the I and B groups are considered as the products, and the minor group of biphenyl derivatives is neglected. Members of I and B groups possess an aromatic ring and are therefore produced in the stoichiometry of one molecule per molecule of reactant. Assuming that the cracking does not go much further (no destruction of the remaining ring in B and I), the total molar concentration in NT, I, and B doea not vary (this is coherent indeed wit h a quantitative, although not very accurate, chromatographic analysis). Therefore the evolution of the reaction has then been followed by recording the relative molar fractions within the set of these three groups. Results are given in Figure 4.

Note that the term "hydrocracking" actually refers here to reactions involving the breakage of an aliphatic chain within the molecule, leading to the formation of a compound of the same number of carbon atoms or having lost a few carbon atoms.

Evolution within the NT Group. The different members of the NT group can be classified into five subgroups as follows: [Nl, naphthalene and tetralin; [ lMN] , 1-methylnaphthalene, 1-methyltetralin, and 5- methyltetralin; [2MNl, 2-methylnaphthalene, 2-methyltetralin, and 6-methyltetralin; [DMNI , dimethylnaphthalenes and corresponding dimethyltetralins; [TMN] , trimethylnaphthalenes and corresponding trimethylte- tralins. (The various isomers of dimethyl- and trimethyl- substituted compounds cannot be identified in the chromatographic analysis within their subgroups.).

The evolution with the contact time of the alkylnaphthalenes is reported in Figure 5. Owing to an incomplete analysis on the CPSIL5 column, the subgroups are represented here by the diaromatics and the only identified di- or trimethylnaphthalenes. Although this is an ap- proximate expression of the evolution of the subgroups, it gives nonetheless the behavior of the system. The quantities of diaromatics are relative to the original 1-methylnaphthalene concentration in the feed.

According to our previous study, 2-methylnaphthalene is formed very quickly as opposed to the other diaromatics and appears as the major primary product as is the case in the hydrocracking under the same conditions using the hydrotreating catalyst of low activity. Naphthalene and dimethylnaphthalenes appear unexpectedly as secondary products. This could be due to a higher reactivity of 2-methylnaphthalene which would then be the main precursor. The trimethylnaphthalenes are formed in smaller quantities and as a secondary (or tertiary) product as the dimethylnaphthalenes are the obvious precursors to their formation.

The main trend is the increase in methylation within the subgroup together with naphthalene formation. This is probably done through a disproportionation process such

methylnaphthalene + methylnaphthalene =

as

naphthalene + dimethylnaphthalene Considering the small quantity of trimethylnaphtha-

lenes, one expects an equivalent quantity of moles of the [N] and the [DMNI subgroups. As can be seen in Figure 4, the quantities of dimethylnaphthalenes and of naphthalene are very similar. Moreover, a careful measurement of these two subgroups using the PONA column indicates that under the reference conditions (contact time of 1 h)

Ind. Eng. Chem. Res., Vol. 32, No. 8,1993 1597 1 .o

z 0 a E 0.5 a

I

6

2

1 .c

z E E 0.5 3 2

a

0.1

1 .c

z 0 a 6 E 0.5 a:

2 I

0.1

0.0 0.5 1 .o 1.5 CONTACT TIME ( h )

1 400 450 TEMPERATURE PC)

40 TOTAL PRESSURE (atrn)

Figure 4. Evolution of reaction with (a, top) contact time (reference conditions), (b, middle) temperature, and (c, bottom) total pressure. (0) Molar fraction of NT group (alkylnaphthalenes and alkyltetralins); (x) molar fraction of I group (alkylindans); (+) molar fraction of B group (alkylbenzenes); (solid lines) recalculated curves after best fitting. the ratio of [Nl to [DMNI is about 1.2. It is then very likely that the disproportionation process is the main source of methylation of the diaromatics.

0.0 0.5 1 .o 1.5 CONTACT TIME (h)

Figure 5. Evolution with contact time of molar fractions of diaromatics relative to 1-methylnaphthalene in feed (reference conditions). (0) 1-Methylnaphthalene; (0) 2-methylnaphthalene; (+) naphthalene; (*) dimethylnaphthalenes; (0) trimethylnaphthalenes.

The isomerization of 1-methylnaphthalene (1MN) into 2-methylnaphthalene (2MN) is relatively fast. Indeed, the rate constant of a pseudo-monomolecular isomerization process is about 6 h-l under the reference conditions whereas that of the global disappearance process is of about 0.9 h-l. Therefore, a thermodynamic equilibrium should be reached with a common rate of disappearance for both diaromatics. A nearly constant value of the ratio of 2MN to 1MN of about 2.4 is indeed observed beyond a contact time of about 0.5 h (cf. Figure 5). The theoretical value of this ratio is about 1.5 (Alberty and Bloomstein, 1985) and is nearly constant in the range of temperatures of this study (380-440 "C). Our experimental values in this range of temperatures vary from 1.6 to 2.4 (at a contact time of 1 h), and a thermodynamic equilibrium is probably then attained.

Evolution within the B Group. A histogram of the various alkylbenzenes is given in Figure 6, obtained under the reference conditions, a t short and moderate contact times. The distribution of aromatics of 6-10 C atoms is similar in both cases, but the proportion of aromatics with 11 C atoms is very high at short contact time. These C11- alkylbenzenes consist of about 75 5% n-pentylbenzene and 25 % methylbutylbenzene. According to our previous study, the same compounds are present in a similar proportion (about 80 and 20 % ) as the only alkylbenzenes and as primary products in the hydrocracking on the hydrotreating catalyst of lower cracking activity under the same experimental conditions. This suggests that in the present case the C11-alkylbenzenes are formed as primary products (probably by opening of the saturated ring of the methyltetralins) and are the precursors of C10- to C6-alkylbenzenes. This is confirmed by the evolution of these compounds with the contact time shown in Figure 7 where C11-alkylbenzenes and the group of alkylbenzenes of lower C atom number exhibit kinetics of the first and second order, respectively.

The hydrocracking of the C11-alkylbenzenes gives mainly C6-, C7-, and C8-alkylbenzenes. Such a distribution of monoaromatics is also observed in the hydrocracking of tetralin under similar conditions, with a low yield in C8 and C9-alkylbenzenes (Haynes et al., 1983). The formation of benzene and toluene occurs through the


0'4 * 0.3 -

2

+ 0 Q a E 0.2- E

2 r

0.1 -

n n ! . . . . . . . . . . . I -.- . . . . . . . . . . . . . 0 1 2 3 4 5 6 7 8 9 1 0 1 1 1 2

NUMBER OF CARBON ATOMS

Figure 6. Molar fractions of alkylbenzenes at short (0.12 h) and moderate (1 h) contact time (reference conditions). (0) Short contact time (0.12 h); (X) moderate contact time (1 h).

0.20 / I I x/ I

0.0 0.5 1 .o CONTACT TIME (h)

Figure 7. Evolution with contact time of molar yield (with respect to initial 1-methylnaphthalene) of C11 and C6410 alkylbenzenes (reference conditions). (0) C11 alkylbenzenes; (+) C6410 alkylbenzenes; (X ) all alkylbenzenes.

breakage of the bond between the aromatic ring and an alkyl (non-methyl) substituent, as has been observed for the ring opening of the methyltetralins reported in our previous study. The formation of ethylbenzene and xylenes suggests an alternative opening between the first and second atom carbons of the alkyl chain. Finally, the low yield in C9 and C10 compounds shows that the breakage of the alkyl chain is difficult beyond the second C atom.

Simplified Kinetic Model of the Hydrocracking of 1-Methylnaphthalene. Justification of the Lumping. In our previous study of the hydrocracking on a hydrotreating catalyst of low cracking activity, it has been found that 1-methylnaphthalene is in equilibrium with the corresponding methyltetralins practically immediately and undergoes about equal isomerization into 2-methylnaphthalene and conversion into alkylindans and alkylbenzenes with conservation of the C atom number.

The reaction in the present study using a hydrocracking catalyst is an extension of the preceding one with the two following modifications: faster processes of hydrocracking and an alteration of the number of carbon atoms of the compounds (essentially a disproportionation for the diaromatics and a decrease for the alkylbenzenes).

The reaction of hydrocracking of 1-methylnaphthalene on the hydrotreating catalyst is mainly its conversion into C11-indans and C11-alkylbenzenes. As the same type of compounds is formed on both catalysts, it appears convenient to carry out a lumping of the reactant and products into three groups which are homologous with respect to the 1-methylnaphthalene (and methyltetralins), C11-indans, and C11-alkylbenzenes, by lumping the products without considering the number of C atoms.

Kinetic Model and Parameters. Taken into account the number of experiments and for simplicity's sake, we consider as in our previous study the simplified kinetic scheme:

Scheme I

where N represents the various alkylnaphthalenes (naphthalene included) within the NT group, in thermodynamic equilibrium with the corresponding alkyltetralines T (tetralin included). The reaction of transformation of members of the NT group is assumed to take place through the breakage of an aliphatic bond in the alkyltetralins. Indeed, hydrocracking of tetralin under conditions similar to the present ones leads to products which compare very well with the products listed in Table I (Haynes et al., 1983). Also, hydrocracking of tetralin on a presulfided nickel-on-silica-alumina leads to the various monoaromatics and light alkanes found in the present study (Flinn et al., 1960); in addition, it is shown that under the same conditions the hydrocracking of n-butylbenzene does not give back tetralin, showing that reaction I11 is not reversible.

In order to express the reaction rate, we assume that the reactions 11-IV take place as pseudo-monomolecular reactions of the adsorbed species on acid sites (the constant rates including the hydrogen pressure). Taking as PG and bo the partial pressure and the adsorption constant of any G group, the specific rate of reaction (in mol-h-l*kg,t-l) can be written, in a Langmuir-Hinshelwood model where the rate-limiting step is the surface reaction, and for example for reaction 11, as

(mol.h-l.kg,;') (1)

where P represents various poisons ("3 in particular) and where the adsorption of saturated compounds is considered to be negligible.

We consider as a further simplifying assumption that the adsorption of monoaromatics T, B, and I are similar with an adsorption constant ~ T B I .

Let Po be the initial pressure in reactant l-methylnaphthalene and a the fraction of alkyltetralins in the NT group; the specific rate of reaction can then be simply

Ind. Eng. Chem. Res., Vol. 32, No. 8,1993 1599

Scheme I1 rewritten with two unknown parameters (terms in brackets) as

As the number of moles of species NT, I, and B is conserved, we can follow the reaction by the relative molar fractions of the three groups XNT, X B , and XI as plotted in Figure 4.

Considering the molar flow F~MN of 1MN at the entrance to the reactor, a nearly constant total molar flow in the reactor, and the change AXmp in the relative molar fraction of NT and I due to reaction I1 over the mass Am of catalyst, we can write

-FIMNAxNT/I = R ~ N T / I A m (3) The rate of reaction 111 can then be expressed considering

the variation of the relative molar fractions with the “contact time” 0, = 1/LHSV as

with the reduced apparent rate constant KTII (h-9,

and adsorption coefficient BNT,

where MIMN is the molar mass of 1MN (kg-mol-’), X ~ M N is the mass fraction of 1MN in the liquid feed, and p, and pfare the density of the catalytic bed and that of the liquid feed, respectively ( k g m 3 .

By carrying out the same transformation for the other reactions, one gets the following simplied kinetic scheme:

Scheme I’

NT-I (1’)

NT-B (11’)

I - B (111’)

with the corresponding reaction rates:

KI/BXI = 1 + (1 - CY)BmXm

(7)

(8)

(9)

with

Thus, the four parllmeters KT/I, KT/B, KI/B,. and BNT Can be determined using a conventional optimization technique so as to get the best fitting of the data with the calculated values obtained by integration of a simple differential system (Scheme 11):

Time Evolution of the Reaction under the Reference Conditions. The best fitting curves, taking a to be about 0.4, are shown in Figure 4a, with the following best-fitting parameters: KT/I = 1.20 h-’; KT/B = 0.90 h-l; KI/B = 1.05 h-l; #am = 0.

The main result is that the parameter PNT is negligible; that is, the fitting is not impeded by omitting the denominator term. The representation of the kinetics as a first order one is then good enough for our set of data. Note that a negligible value for does not imply a weak adsorption of the compounds but rather implies the approximation of a similar adsorption constant bmBI for all aromatic compounds. AS the value8 Of the rate Constants KT/B and KI/B

corresponding to similar reactions (opening of the saturated ring) are similar, a common value KTI/B (here of about 1 h-l) will be assumed for the further optimizations. The influence of the temperature and pressure will then be analyzed using the following simplified mechanism (Scheme I”) with only two unknown rate constants:

Scheme I”

NT-I (1”)

NT-B (11”)

I - B (111”)

with

%,I = ‘YKT/IXNT (18) RNT/B = “%I/BXNT (19)

RI/B = KTI/BXI (20) This simplified kinetic scheme is pictured in Figure 8.

Effect of the Temperature around the Reference Conditions. The effect of the temperature T has been studied by assuming the preceding values of the parameters at 400 OC and searching for the best fitting apparent activation energies. The variation of a is directly bound to the hydrogenation enthalpy which was taken to be about -30 kcal.mo1-l. The recalculated curves are shown in Figure 4b with the following best-fitting apparent activation energies for KT/I and KTI/B: ET11 = 39 kcal-mol-l; ETI B = 38 kcal*mol-l.

dhese activation energies are very close, which suggests a common difficult step in reactions such as the formation of an unstable carbocationic intermediate. Note that the apparent activation energies express the effect of temperature on both the adsorption constant and the actual kinetic rate constant of the surface reaction.


NT group I group

C1 l-alkylindans

2-methylnaphthalene hydrindanes ?

naphthalene

KTVB = 1.0 h - l ETVB = 38 kcal.mo1.l

B group

C1 l-alkylbenzenes

BTX + alkanes

t H 2 i

alkylcyclohexanes

Figure 8. Schematic kinetic mechanism for hydrocracking of l-methylnaphthalene at moderate conversion yield (dashed arrows refer to slow processes).

The increase in the temperature favors the kinetics of the reaction of T and I but decreases the proportion a of alkyltetralins within the NT group. Thus the total apparent activation energy of the reaction is lower than the above values, being of about 21 kcal.mol-l.

Effect of the Pressure around the Reference Conditions. This effect has been studied by assuming an order n relative to the partial hydrogen pressure (which is proportional to the total pressure). The corresponding term is assumed to be included in each apparent reduced rate constant K . The parameter a was modified accordingly to the mass law. The recalculated molar fractions are shown in Figure 412, with the following best-fitting values of the order nT/I = -0.5 and nTI/B = 0.06.

These results are to be discussed with care considering the poor fitting of the data. The hydrogen partial pressure has a small effect on the reactions of ring opening of the alkyltetralins and alkylindans but a slightly inhibiting effect on the isomerization of the alkyltetralins into alkylindans. One would expect a positive effect of hydrogen on the ring opening, which is not the case. In any case, it appears that the effect of hydrogen is to favor the ring opening as opposed to the isomerization process.

Note that the increase in hydrogen pressure will accelerate the reaction rate on the whole by increasing the fraction a of alkyltetralins within the NT group. There is indeed an apparent pseudo order of about 1 on this coefficient a around the reference conditions.

Inhibition by the Aromatics

The occupation of the active sites by 1MN and the products of its hydrocracking is shown by the inhibition of n-heptane hydrocracking. This reaction is easily monitored by the isomerization into methylhexanes. By assuming a low adsorption of the alkane and first-order kinetics, and considering a low reaction yield, the reciprocal of this yield of hydroisomerization is expected to vary linearly with the diaromatic initial pressure. As shown in

0 1 2 3 4 P"(atrn)

Figure 9. Variation of reciprocal of yield of n-heptane hydroisomerization with initial partial pressure of l-methylnaphthalene, Po (contact time 0.5 h, otherwise reference conditions).

Figure 9, this relationship is obeyed and leads to the ratio

bNTBIP" 1 + bpPp

by assuming the common adsorption constant bmsl for all the aromatic compounds.

The high adsorption of the aromatic is also shown by the evolution of the yield of the NT group conversion, x, with the initial pressure P" in 1MN. Integration of relationship 18 leads to

Aset of four runs have been carried out where the contact time 6, and the partial pressure in poisons, Pp, have been kept constant (e, = 0.5 h and the partial pressures according to the reference conditions) while the mass fraction of 1MN in the liquid feed, X ~ M N , has been allowed to vary by replacing part of this reactant by n-heptane.

Under these conditions, PO is proportional to X ~ M N so that the term PO in the denominator of relationship 22 vanishes. Thus, the right-hand term becomes a linear function of P". This linear variation is followed as shown in Figure 10 and leads to the ratio

(23)

There is a qualitative agreement between relationship 21 and 23, and it has to be noted that they refer to two different reactions: hydrocracking of n-heptane and hydrocracking of 1MN.

In conclusion, adsorption by 1MN and its conversion products is very important. Note that this is not in disagreement with a first-order kinetic scheme of the hydrocracking of 1MN as long as we assume a similar adsorption for the reactant and the products contained in groups T, B, and I.


A

0 ' I I I 1 0 1 2 3 4

Po (atm) Figure 10. Effect of initial partial pressure of 1-methylnaphthalene PO on reaction yield x of ita conversion (contact time 0.5 h, otherwise reference conditions).

Inhibition by Nitrogen and Sulfur Compounds

The LCO contains an important quantity of nitrogen- containing compounds, with a concentration in N of about 500 ppm. The presence of these compounds is simulated in our synthetic feed by NH3 arising from the fast decomposition of n-butylamine present in the liquid feed (480 ppm w/w nitrogen under the reference conditions). Due to their basicity, these compounds are likely to adsorb strongly on the acid sites and thus inhibit the hydrocracking. In the present range of temperature and on zeolitic catalysts, this inhibiting adsorption can be considered as reversible as observed in the case of n-heptane hydrocracking (Corma et al., 1987; Dufresne et al., 1990). Similarly, sulfur compounds (1.4% S w/w in the reference feed) are likely inhibitors.

The partial pressures of NH3 and H2S have then been varied around the values in the reference conditions so as to estimate the inhibition effect. From relationship 2 the reciprocal of reaction rates must vary linearly with the reciprocal of the partial pressures of the poisons. The results are shown in Figure 11 in the case of several reaction rates and both poisons ("3 or HzS), rates and partial pressures being relative to the values under the reference conditions. The inhibiting effect has been followed on the isomerization of n-heptane, on the disappearance of the NT group (reactants), and on the formation of the B and I groups. The effect of the inhibitors is about the same for the four rates, suggesting a unique or major active acid site. The inhibition by N is much higher than it is by S, the ratio of the adsorption constants being estimated here to about 26 for NH3 and H2S.

Taking into account the rate of reaction in the absence of inhibitors (by extrapolation), the inhibiting effect under the reference conditions leads to a decrease of the reaction rate of about 30%. One can expect an inhibiting effect by the N and S compounds of similar importance to the hydrocracking of LCO.

Note that this relatively low inhibiting effect indicates that the compound adsorption term bpPp of the N and S compounds (poisons) verifies the following relationship under the reference conditions:

0.0 0.5 I .o 1.5 2.0 RELATIVE INHIBITOR CONCENTRATION

5

Figure 11. Influence of N and S compounds on the rates of varioua processes. (full line) Inhibition by NHs; (broken line) inhibition by HsS; (0) disappearance of NT group; (+) formation of alkylbenzenes; (X) formation of alkylindans; (2) isomerization of n-heptane.

by assuming the common adsorption constant ~ N T B I for all the aromatic compounds.

It appears, however, that the numerical values determined for relationships 24 and 21 or 23 are not consistent enough. This can be attributed to the simplification of the kinetic scheme and/or a variety of active sites. Under the reference conditions, it can be estimated, however, that most active sites are occupied with, for example, three- fourths of the occupation by the aromatics and one-fourth by the poisons. Then, inhibition by NH3 and H2S does exist but is moderate compared with the autoinhibition by the aromatic compounds.

Conclusion

The catalytic hydrocracking of our synthetic model LCO can be considered as the conversion of a mixture of alkylnaphthalenes and alkyltetralins in thermodynamic equilibrium under our operating conditions. Alkyltetraliis transform into alkylindans by isomerization and alkylbenzenes by opening of the saturated ring of the alkyltetralins. These alkylindans undergo the ring opening themselves as in the case of the alkyltetralins. There are also processes of conversion within these groups: the alkylnaphthalenes-alkyltetralins undergo a methylation and a demethylation whereas the alkylbenzenes undergo a partial dealkylation to give BTX compounds.

Both H2S and NH3 have an inhibiting effect on all acidic catalyzed reactions, suggesting a unique type of acidic site. Inhibition by NH3 has been found much stronger than that by H2S. However, the aromatics have a higher inhibiting effect on the hydrocracking as shown by the reduction of the n-heptane hydrocracking and the autoinhibition of the reaction.

As a small amount of alkanes is formed, hydrocracking of diaromatics into branched monoaromatics is a possible way to improve the quality of LCO by desulfurization, denitrogenation, hydrogenation of diaromatics into naphtheno-monoaromatics, as well as isomerization and ring opening of naphtheno-monoaromatics. Severe operating


conditions, Le., high pressure, high temperature, and long contact time, will be yet needed.

Nomenclature Compounds 1MN = 1-methylnaphthalene 2MN = 2-methylnaphthalene xMT = x-methyltetralin ( x = 1, 2, 5, 6) xMD = x-methyldecalin ( x = 1, 2) DMDS = dimethyl disulfide NBA = n-butylamine

Groups A = low carbon number alkanes (n-heptane and isomers and

B = alkylbenzenes and alkylcyclohexanes (benzene and

BP = alkylbiphenyls I = alkylindans (indan included) N = naphthalene and alkylnaphthalenes with NT NT = alkylnaphthalenes and alkyltetralins (naphthalene and

T = tetralin and alkyltetralins with NT TI = joined groups T and I P = poison in feed

Subgroups within the NT Group [N] = naphthalene and tetralin [ l M N ] = 1-methylnaphthalene, 1-methyltetralin, and 5-

[2MNl = 2-methylnaphthalene, 2-methyltetralin9 and 6-

[DMNI = dimethylnaphthalenes and corresponding di-

[TMN] = trimethylnaphthalenes and corresponding tri-

Latin Symbols bo = adsorption constant of any group G (atm-l) bGlGz = common mean adsorption constant of group G1 and

G2 EGIIG~ apparent activation energy on the reaction of trans-

formation of group G1 into group G2 F~MN = molar flow of 1-methylnaphthalene at the entrance

of the reactor AH'TN = standard enthalpy of hydrogenation of methyl-

naphthalenes into the parent methyltetralins k , ~ l / ~ z = specific rate constant of pseudo-first-order trans-

formation of group G1 into group G2 (mol.h-l.kgat-l) KTN = equilibrium constant for the hydrogenation of me-

thylnaphthalenes into the parent methyltetralins (atm-2) M1m = molecular mass of 1-methylnaphthalene (kg-mol-1) nG1p = order of the reaction of transformation of group G1

into group 62, with respect to hydrogen pressure Po = partial pressure in group G (atm) Po = partial pressure of 1MN at the entrance of the reactor

(atm) R G ~ / G ~ = specific rate of transformation of group G1 into

group G2 (mol.h-1.kgCat-') T = temperature (K) T / N = molar ratio of alkyltetralins to parent alkylnaphtha-

lenes XTN = molar ratio of total methyltetralins to parent meth-

ylnaphthalene X ~ M N = mass fraction of 1-methylnaphthalene in the liquid

feed

Greek Symbols a = molar fraction of monoaromatics T within the NT group

alkanes of lower mass)

cyclohexane included)

tetralin included)

methyltetralin

methyltetralin

methyltetralins

methyltetralins

/3m = reduced adsorption constant (dimensionless) BC = "contact time" ('h-1") KGl/G2 = reduced apparent rate constant of pseudo-first-order

pc = density of the catalytic fed (kg-m-9 pf = density of the liquid feed ( k g m a ) y. = yield of the NT group conversion

transformation of group G1 into group G2 (h-1)

Literature Cited

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Bastick, M.; Bastick, J.; Perrot, J. M.; Ayadi, A. Hydroconversion d'hydrocarbures I-Hydrocraquage thermique du squelette naph- thalhique. Entropie 1988,137,93-101.

Benson, S . W. Methods for the estimation of thermochemical data. In Thermochemical kinetics, 2nd ed.; Wiley: New York, 1976; Chapter 10, pp 19-77.

Bouchy, M.; Dufresne, P.; Kasztelan, S. Hydrogenation and Hydro- cracking of a Model Light Cycle Oil Feed. 1. Properties of a Sulfided NiMo Hydrotreating Catalyst. Znd. Eng. Chem. Res.

Corma, A.; Fortes, V.; Monton, J. B.; OrchiUes, A. V. Catalytic cracking of alkanes on large pore, high SiOa/Al2Os zeolites in the presence of basic nitrogen compounds. Influence of catalyst structure and composition in the activity and selectivity. Znd. Eng. Chem. Res.

Dufresne, P.; Bigeard, P. H.; Billon, A. New developments in hydrocracking: low pressure high-conversion hydrocracking. Catal. Today 1987, I, 367-84.

Dufresne, P.; Quesada, A.; Mignard, S. Influence of nitrogen feed content on the performances of a zeolite hydrocracking catalyst. Stud. Surf. Sci. Catal. 1990,53, 301-315.

Fischer, R. H.; La Pierre, R. B.; Shih, S. S.; Varghese, P. Production of high octane gasoline. U.S. Patent 4,828,677, 1989.

Flinn, R. A.; Larson, 0. A.; Beuther, H. The mechanism of catalytic hydrocracking. Znd. Eng. Chem. 1960,52, 153-156.

Frye, C. G.; Weitkamp, A. W. Equilibrium hydrogenations of multi- ring aromatics. J. Chem. Eng. Data 1969,14, 372-376.

Haynes, H. W., Jr.; Parcher, J. F.; Helmer, N. E. Hydrocracking polycyclic hydrocarbons over a dual-functional zeolite (faujasite)- based catalyst. Znd. Eng. Chem. Process Des. Deu. 1983,22,401- 409.

Huang, C. S.; Wang, K. C.; Haynes, H. W., Jr. Hydrogenation of phenanthrene over a commercial cobalt molybdenum sulfide catalyst under severe reaction conditions. In Liquid fuels from coal; Ellington, R. T., Ed.; Academic Press: New York, 1977; pp

Sawyer, W. H.; Hudson, C. W. Process for the production of ultra high octane gasoline, and other fuels from aromatic distillates. U.S. Patent 4,828,675, 1989.

Perrot, J. M.; Ayadi, A.; Bastick, M.; Bastick J. Upgrading of coal pyrolysis products: catalytic hydrocracking of bicyclic compounds. Fuel Process. Technol. 1988,20,223-232.

Qader, S . A.; Hill, G. R. Development of catalysts for the hydrocracking of polynuclear aromatic hydrocarbons. P r e p . Pap.-Am. Chem. SOC., Div. Fuel Chem. 1972,16,93-106.

Quesada-Perez, A. M. tramformation dun-heptanesur un catalyaeur zklithique d'hydrocraquage en prbence d'hydroghe sulfur& Thesis, Universit4 de Paris VI, 1989.

Vasquez, M. I.; Escardino, A.; Corma, A. Activity and selectivity of NiMo/HY ultrastable zeolites for isomerization and hydrocracking of alkanes. Znd. Eng. Chem. Res. 1987,26, 1495-1500.

Wuu, S. K.; Hatcher, W. J., Jr. Zeolite catalyst for hydrocracking polynuclear aromatic-phenanthrene kinetics. Presented at the AIChE Spring National Meeting, Houston, 1983.

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1987,26,882-886.

63-78.

Received for review October 26, 1992 Revised manuscript received April 1, 1993

Accepted April 20, 1993

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