Ind. Eng. Chem. Res. 1988,27, 2039-2043
e,,
= fractional coverage of component j i n CSTR k = stoichiometric coefficient of component j , reaction i vl = turnover frequency of reaction 1, s-l vHD = turnover frequency of the H2/D2 exchange reaction, T = residence time of an inert component in the catalyst bed, S
Registry No. Ni, 7440-02-0; NiS, 11113-75-0; Pd, 7440-05-3; 2-ethylhexenal, 645-62-5.
Literature Cited Al-Ammar, A. S.; Webb, G. “Hydrogenation of Acetylene over Supported Metal Catalyst. Part I”. J. Chem. SOC.,Faraday Trans 1 1978, 74, 195. Berndt, G. F.; Thomson, S. J.; Webb, G . “Hydrogenation of Acetylene over Supported Metal Catalyst. Part IV”. J. Chem. Soc., Faraday Trans 1 1983, 79, 195. Blyholder, G.; Shihabi, D. “Infrared Spectral Observation of the Interaction of Acetone with Silica-Supported Ni and Con. J. Catal. 1977, 46, 91. Boeseken, J.; van Senden, G. H. “Zerstijrung des Heptylalkohols bei 220’ in Ggw. von fein verteiltem Nickel”. Red. Trav. Chim. Pays-Bas 1913, 32, 23. Chaudhari, R. V.; Jaganathan, R.; Kohle, D. S.; Emig. G.; Hoffmann, H. ”Kinetic Modelling of a Complex Consecutive Reaction in a Slurry Reactor: Hydrogenation of Phenyl Acetylene”. Chem. Eng. Sci. 1986, 41, 2696. Froment, G. F.; Hosten, L. “Catalytic Kinetics: Modelling”. In Catalysis; Springer Verlag: Berlin, 1981; Vol. 2, p 98. Grant, J.; Moyes, R. B.; Oliver, R. G.; Wells, P. B. “The Hydrogenation of Alkadienes. Part VII”. J. Catal. 1976, 42, 213. Hemidy, J. F.; Gault, F. G.; “RBactions de Contact du butanal sur Chim. Fr. 1965, 1710. Film de Palladium”. Bull. SOC. HlavaCek, V.; Votruba, J. In Chemical Reactor Theory, a Reuiew; Lapidus, L., Amundson, N. R., Eds.; Prentice-Hall: Engelwood Cliffs, NJ, 1977; Chapter 6. Jobson, E.; Smedler, G. “Infrared Investigation of 2-Ethyl-Hexenal and 2-Ethylhexanal Adsorbed on Working Ni/Si02 and NiS/Si02 Catalysts”. Submitted for publication in J. Catal. 1988. Konvalinka, J. A.; van Oeffelt, P. H.; Scholten, J. J. F. “Temperature Programmed Desorption of Hydrogen from Nickel Catalysts”. Appl. Catal. 1981,1, 141.
2039
Lee, H. C.; Butt, J. B. “Kinetics of the Desulfurization of Thiophene: Reactions of Thiophene and Butene”. J. Catal. 1977, 49, 320. Magnusson, J. “H2/D2Exchange as a Model Reaction for Studying Hydrogen Adsorption on a-A1203-SupportedCopper and Nickel Catalysts”. Ind. Eng. Chem. Res. 1987,26, 874. Newham, J.; Burwell, R. L. “Reactions between Secondary Alcohols, Ketones, and Hydrogen on Metallic Catalysts”. J. Am. Chem. SOC. 1964,86, 1179. Niklasson, C.; Smedler, G. “Kinetics of Adsorption and Reaction for the Consecutive Hydrogenation of 2-Ethylhexenal on a Ni/Si02 Catalyst”. Ind. Eng. Chem. Res. 1987, 26, 403. Patterson, W. R.; Burwell, R. L. “Isotopic Exchange Reactions Involving Alcohols, Ketones and Deuterium on Silica, on Palladi1971, 93, 833. um/Silica, and on Alumina”. J. Am. Chem. SOC. Phillipson, J. J.; Wells, P. B.; Wilson, G. R. “The Hydrogenation of A 1969, 1351. Alkadienes. Part 111”. J. Chem. SOC. Smedler, G. “Selective Hydrogenation of 2-Ethylhexenal. 1. Analysis of Sorption Kinetics for 2-Ethylhexenal and 2-Ethylhexanal on Working Ni/Si02, NiS/Si02, and Pd/Si02 Catalysts”. Znd. Eng. Chem. Res. 1988, preceding paper in this issue. Smedler, G. “Kinetic Analysis of the Liquid Phase Hydrogenation of 2-Ethylhexenal in the Presence of Supported Ni, Pd and NiS Catalysts”. Can. J. Chem. Eng. 1987, in press. Somorjai, G. A. “Active Sites in Heterogeneous Catalysis”. Adu. Catal. 1977, 26, 2-68. Suen, T.-J.; Fan, S. “Catalytic Hydrogenation of Heptaldehyde in Vapor Phase”. J. Am. Chem. SOC. 1942, 64, 1460. Tanaka, K. “Studie? in Surface Science and Catalysis”. In Catalytic Hydrogenation, Cerveny, L., Ed.; Elsevier: Amsterdam, 1986; Vol. 27. Thomson, S. J.; Wishlade, J. L. “Radiochemical Studies of Chemi1962,58, sorption and Catalysis. Part IV”. Trans. Faraday SOC. 1170. Tsuji, J.; Ohno, K.; Kajimoto, T. “Organic Synthesis by Means of Noble Metal Compounds. Part XX”. Tetrahedron Lett. 1965, 4565. Webb, G. In Comprehensive Chemical Kinetics; Bamford, C. H., Tipper, C. F. H., Eds.; Elsevier: Amsterdam, 1978; Vol. 20. Young, R. P.; Sheppard, N. “Infrared Spectroscopic Studies of Adsorption and Catalysis. Part V”. J. Catal. 1971, 20, 340. Received f o r review November 17, 1987 Accepted June 13, 1988
Hydrocracking of n -Heptane with a NiO-Mo03/HY Ultrastable Zeolite as Catalyst. The Network of the Reaction M. Isabel Vgzquez, Agustb Escardino,* and Antonio Aucejo Departamento de Ingenierla Qujmica, Uniuersitat de Valdncia, Doctor Moliner, 50, 46100 Burjassot, Valencia, Spain
The hydrocracking of n-heptane has been studied in a continuous, tubular, plug flow reactor using a 4 wt % Ni0-8 wt % MoO,/HYUS zeolite as catalyst, to try to obtain a network of reactions to account for the formation of the various products observed. In view of the products obtained and depending on whether they are primary or secondary, a series of simultaneous parallel reaction schemes have been proposed to explain the network of the reaction. The kinetic parameters of these reactions have been obtained from the initial selectivities of the products. The values of the apparent activation energies obtained for the isomerization, hydrogenolysis, cracking, and disproportionation reactions were 99.1, 169.6, 221.4, and 195.9 kJ/mol, respectively. Hydrocracking is a c o m b i n a t i o n of cracking and hyd r o g e n a t i o n which is carried out at relatively h i g h pressures and temperatures lower than catalytic cracking. At these operating conditions, the isomerization reactions are more favored than those of cracking. In any case, the extent of these reactions can be varied by a d e q u a t e l y se-
* T o whom correspondence should be addressed. 0888-5885/88/2627-2039$01.50/0
lecting t h e o p e r a t i n g conditions and varying the hydrog e n a t i o n f c r a c k i n g r a t i o of the catalyst. In the hydrocracking of hydrocarbons, a large number of simultaneous, parallel, and consecutive reactions take place (Langlois and Sullivan, 1970). In order to s t u d y these reactions, t h e initial selectivities method could be applied. This procedure has been satisfactorily employed to s t u d y n-heptane cracking on CrHNaY and HY zeolite catalysts
0 1988 American Chemical Society
2040 Ind. Eng. Chem. Res., Vol. 27, No. 11, 1988
(Lbpez Agudo et al., 1981; Corma et al., 1984). In accordance with this method, the initial selectivity of a product (number of moles obtained from each n-heptane mole reacted) can be calculated as the slope of the tangent at zero conversion to the curve representing the variation of a product yield versus the corresponding total conversion (Best and Wojciechowski, 1977). From the shape of these curves, it can also be determined whether the observed products are primary or secondary, and from these results, a possible network for the reaction can be proposed. In addition, from the initial selectivities of the products, the selectivities of the individual reactions and their kinetic parameters can be calculated. In the present work, the hydrocracking of n-heptane with a bifunctional NiO-MoO,/HY ultrastable zeolite catalyst has been studied, and the initial selectivities procedure has been used to study the kinetics and the selectivity of the various types of reactions proposed, thereby proving the validity of this procedure. Experimental Section Materials. The catalyst used for this study was an ultrastable zeolite impregnated with NiO and Moo3 The HY ultrastable zeolite (ao = 24.4 A, measured by X-ray diffraction) was prepared by repeated ion exchange in an ammonium acetate solution of the sodium form of a Linde SK-40 zeolite (Union Carbide) (Si/Al = 2.4, measured by analysis after fusion of the solid and X-ray diffraction). This was followed by deep bed calcination at 823 K for 3 h. The process was repeated until the final Na+ content of the zeolite (determined by atomic absorption spectroscopy of the final product after fusion of the solid by a conventional technique) was lower than 2% of the initial value. The BET area of the ultrastable zeolite (HYUS) was 450 m2/g. The nickel and molybdenum were incorporated into the zeolite by vacuum impregnation at 343 K from an aqueous solution of nickel nitrate and ammonium heptamolybdate, respectively. After each impregnation, the sample was dried at 383 K for 6 h and then calcinated in two steps. The first, to decompose the salt, was carried out in an air flow at 723 K for 2 h and the second at 823 K for 3 h. The final NiO and Moos content of the catalyst, determined by atomic absorption spectroscopy, was 4 and 8 wt %, respectively. Apparatus. The experiments were carried out in a continuous, tubular, plug flow, stainless steel reactor of 40 cm length and 2 cm internal diameter. The apparatus has been described in detail in a previous work (VBzquez et al., 1986). Procedure. The experiments have been carried out at an absolute pressure of 2.45 MPa, hydrogenln-heptane molar ratio of 5.0 (to secure an hydrogen excess), and temperatures of 573,588,603 and 623 K. In each experiment, the W / F oratio (weight of catalyst/molar flow of n-heptane fed) was varied between 75 and 1600 kgs-kmol-’ to obtain different conversions. Several experiments were repeated to check the validity of the results obtained. After preparation the catalyst was pelletized, crushed, and sieved, and particle size fractions of 0.125-0.250 mm were selected. Before introducing it into the reactor, the catalyst was mixed with glass chips of the same particle size in order to keep the volume of the bed constant in all the experiments (2.0 cm3) and to minimize the thermal effects due to the reaction. Then, the system was pressurized with an H2stream, and the temperature was raised to 823 K and then kept at that temperature for 2 h. After this pretreatment, the temperature was set to the desired reaction temperature, the hydrogen flow was regulated, and
Table I. Initial Selectivities of the Different Reaction Products temperature, K product 573 588 603 623 methane 0 0.011 0.013 0.018 ethane 1 x 10-3 2.5 x 10-3 1.25 x 10-3 3 x 10-3 0.024 0.025 0.111 propane 0.026 0.125 isobutane 0.027 0.022 0.043 6X 7.8 X 0.021 n-butane 2 X 0 0 0 butenes 0 0.021 isopentane 2 X 1.9 X 6X n-pentane 3 x 10-3 0.010 7.8 x 10-3 0.018 0 0 0 0 pentenes 0.015 2-methylpentane 2 X low3 3.5 X 7.5 X 8X 3-methylpentane 1 X 3X 4.5 X n- hexane 0.016 0.034 0.0224 0.038 2-methylhexane 0.396 0.380 0.373 0.309 0.405 3-methylhexane 0.487 0.493 0.480 0.071 0.053 0.053 0.064 other X 7 ’ s
the hydrocarbon flow was started. The n-heptane was vaporized and mixed with hydrogen; then the reactants were preheated and fed into the reactor. The products were cooled and the liquid fraction was separated from the gas fraction and then collected in different sampling collectors. In each run, four liquid and gas samples were collected for different times on stream (T.O.S.) and then analyzed. The liquid products were analyzed by gas-liquid chromatography using a 4.3-m column with silicone gum rubber (SE-30) on Chromosorb P at a temperature program of 353-443 K. The gas products were analyzed with a 2-m column of silica gel and Porapak Q at temperatures of 343 and 443 K. The molar yield curves for different cat/oil (weight of catalyst/weight of n-heptane fed for a time on stream) ratios were obtained from the graphs, obtained experimentally from the conversion and the molar yield of a product versus the time on stream at different W/Foratios, by cat =
oil
w _-
1
1
Fo T.O.S. Mn-heptane
where M is the molecular weight. Results and Discussion The Pathway of the Reaction. In Figure 1 the variation of the molar yields of the different reaction products is plotted versus the corresponding total conversion at 623 K and at different cat/oil ratios. From the shape of these curves, we can state that, except butenes and pentenes, all the products of the reaction are primary (because their initial selectivities are different from zero); i.e., all the saturated products of reaction are primary and we can obtain the initial selectivity value for each product as the slope of the tangent at zero conversion. These values are given in Table I. In view of the type of products obtained, the reaction network proposed should include isomerization reactions, to explain the formation of some n-heptane isomers; cracking reactions, because fractions shorter than C7 are present in the products; and a hydrogenolysis reaction, to account for the formation of methane (difficult to explain by an acid p-scission cracking mechanism). Moreover, the results presented in Table I show that the initial selectivity of C,, C6, and C4 fractions is greater than that of C1, C2, and C3 fractions. In order to explain these results, it could be that disproportionation followed by cracking reactions also occurs, as suggested by other authors (Bolton and Bujalski, 1971). Among all the possible disproportiona-
Ind. Eng. Chem. Res., Vol. 27, No. 11, 1988 2041 03
METHANE
0.5 l
.
O
o,2
k
t t
O3I
ETHANE
0.2
o.l 10
30
20
10
40
20
30
LO
u 10
I
.s .s -
t
‘C 10
20
10
LO
30
20
30
LO
10
PENTENES
20
30
05
40
10
20
30
LO
10
20
30
LO
3MPENTANE
10
05
10
20
30
40
0
‘oE a
15t 3MHEXANE
0.1
10
1.0
I
20
10
40
30
lSOPENTANE
10
20
5
10
30
I
20
30
LO 10
20
30
LO
10
20
30
40
n-PENTANE
6 1 OTHERS i-C,
10
40
20
30
40 10
TOTAL CONVERSION
20
(‘/e)
30
LO
TOTAL CONVERSION
(‘/el
Figure 1. Selectivity plots for products obtained during hydrocracking of n-heptane on a 4 wt % Ni0-8 w t % Mo03/HYUS catalyst at 623 ( 0 ) 2 X low3,(A)3 X K. Cat/oil ratios: (0) 1.2 X
tion-cracking reactions the following ones, being the most probable, have been considered: (1\ \-I
- -
2C7 [C14] 2C5 + C4 (3) Therefore, the network of the reaction proposed to explain the product distribution observed experimentally could be
c7
isomerization
i-C7
(4)
+ c5
(5)
+ c4
(6)
’c1+ c.5
(7)
-c2 cracking
c7 c7
-c3 cracking
hydrogenolyais c 7
disproportionation
’c6 + 2c4
(1)
’c6 + c5 + c3
(2)
2c7 2c7
disproportionation
disproportionation
2c7 2C5 + C4 (3) In Table I1 the initial selectivities of the various reaction fractions, obtained from the initial selectivities for products with the same carbon number, are given. From these values and the network of the reaction proposed, it is possible to calculate the initial selectivities of the parallel reactions proposed. For this calculation, we must take into account that, in accordance with the network proposed, the C3, C4, C5, and c6 fractions can be formed by various reactions simultaneously, while the i-C7, C1, and C2 frac-
Table 11. Initial Selectivities of the Different &action Fractions temDerature. K fraction 573 588 603 623
c1
c2 c3 c4
c6 C6
i-CT
0 1 x 10-3 0.026 0.029 0.005 0.019 0.936
0.011 2.5 x 10-3 0.024 0.028 0.0119 0.0405 0.926
0.013 1.25 x 10-3 0.025 0.0508 0.0138 0.0344 0.917
0.018 3 x 10-3 0.111 0.146
0.039 0.061 0.785
tions are formed only by one reaction. Therefore, the initial selectivities of the isomerization and hydrogenolysis reactions are given directly by the initial selectivities of isomerization products (i-C7 fraction) and methane, respectively. On the other hand, the initial selectivity of ethane is equal to the initial selectivity of reaction 5, and the initial selectivity of methane is equal to the initial selectivity of reaction 7 . Initial selectivities of reactions 1 , 2 , 3 , and 6 can be obtained from the following relations: (1SCB)D = (ISC3)T - (Isc3)C = IS(2) (8) (Isc4)D = (ISC4)T - (Isc4)C = ZIs(1) + IS(3) (9) (ISC5)D = (ISC5)T - ( I s c , ) c = IS(2) + 2IS(3) (10) (ISC6)D = (Isc6)T - (ISC6)H = Is(1) + IS(2) (11) where subscripts D, C, H, and T refer to the initial selectivity of that fraction obtained by disproportionation, cracking, and hydrogenolysis reactions and total selectivities, respectively. Taking into account that the initial selectivities of the C3 and C4 fractions by cracking (reaction 6) are the same and that (ISC5)c = (ISC2)T and (ISC6IH= (ISCJT, from
2042 Ind. Eng. Chem. Res., Vol. 27, No. 11, 1988
.^
Table 111. Initial Selectivities of t h e Parallel Reactions Considered temperature. K reaction 573 588 603 623 isomerization 0.936 0.926 0.917 0.785 0 hydrogenolysis 0.011 0.013 0.018 cracking 0.013 0.020 0.094 0.017 0.036 0.049 0.102 disproportionation 0.059 total selectivity 0.985 1.013 0.999 0.999 Table IV. Rate Constant for the n -Heptane Hydrocracking Reaction temp, K k [So], kmol/ (s.kg.Pa) 573 7.03 X 588 11.94 X lowlo 603 20.65 X 623 44.13 x
eq 8-11 it is possible to calculate the initial selectivities of reactions 1, 2, 3, and 6. From these values the initial selectivities for the isomerization, cracking, hydrogenolysis, and disproportionation reactions can be calculated by the following relations: (IS), = IS(4) (12) (1S)c = IS(5) + IS(6) (13) (14) (1S)H = IS (7) (ISID = 2[IS(1) + IS(2) + IS(3)] (15) These values are given in Table 111. In the last row of this table, it can be observed that the sum of the initial selectivities of the proposed reactions is close to 1, for the four temperatures studied. This fact indicates that the network of the reaction proposed agrees well with the experimental results. The initial selectivities for the four parallel reactions proposed have been represented versus temperature in Figure 2. It can be observed that the initial selectivities of cracking, hydrogenolysis, and disproportionation reactions increase with temperature, while the initial selectivity of the isomerization reactions decreases. This fact is very interesting because it suggests that the reaction temperature can be adequately varied to obtain a type of product more selectively. Kinetics of the Parallel Reactions Considered. The initial selectivity of a given reaction is defined as the ratio between the initial rate of the given reaction and the initial rate of the global reaction (Villermaux et al., 1980): (1S)i = rio/ro (16) In accordance with this definition, the rate constant of a reaction can be calculated if the initial selectivity and rate equation of the reaction as well as the rate constant and the rate equation of the global reaction are known. In Table IV the rate constant values obtained in a previous study about the kinetics of the hydrocracking of n-heptane using the same catalyst and in the temperature range of the present work are shown (Vhquez et al., 1988). In that study, it was concluded that the global disap-
'"I
575
625
Figure 2. Variation of the initial selectivity of the parallel reactions considered versus the temperature. (0) Isomerization, (0)hydrogenolysis, (A)cracking, (v)disproportionation.
pearance of n-heptane and isomerization reactions could be satisfactorily described by a pseudo-first-order equation. Therefore, to apply eq 16, a pseudo-first-order equation for the cracking and hydrogenolysis reactions will be considered (Corma et al., 1984; Yates et al., 1964). Nevertheless, for the disproportionation reaction, which demands two adjacent acid sites, a second-order equation will be assumed in accordance with other studies (Guisnet et al., 1985; Absil et al., 1984). Therefore, the initial selectivities of each reaction can be expressed as
kdS01 (IS), = k[Sol
and
where k is the rate constant for a reaction and [So] is the initial concentration of active centers in the catalyst, and p o (partial pressure of n-heptane in the feed) can be calculated from the total pressure (P) and H2/n-heptane molar ratio in the feed ( R M )as D
1
(21)
=
In Table V the rate constants obtained by this procedure for the various reactions considered are given. The rate constants for the isomerization reaction obtained in another study (Vbquez et al., 1988) at the same temperature as the present work are shown in parentheses. The coincidence between these and the values obtained in the present work seems to indicate the consistency of the
Table V. Kinetic Constants, ki[S,] (kmol/(kg* s *Pa)), for t h e Parallel Reaction Considered temperature, K reaction 573 588 603 isomerization 6.58 X 1.10 x 10-9 1.89 x 10-9 (6.15 X (9.11 x 10-10) (1.65 x 10-9) hydrogenolysis 1.13 X lo-" 2.68 x lo-" cracking 9.14 x lo-'* 2.03 X lo-" 4.13 X disproportionation" 6.20 x 10-17 1.73 x 2.48 X "The ki[So] units for this reaction are kmol/(kg.s.Pa*).
600 TEMPERATURE ( K )
623 3.46 x 10-9 (3.16 X lo*) 7.94 x 10-11 4.15 X 1.10 x 10-15
Ind. Eng. Chem. Res., Vol. 27, No. 11, 1988 2043 Table VI. Frequency Factors and Apparent Activation Energies for the Parallel Reactions Considered reaction A , kmol/ (kpwPa) E , kJ/mol isomerization 0.719 99.1 hydrogenolysis 13333 169.6 1.05 x 109 221.4 cracking disproportionation" 4.3 x 10-2 195.9 "The A units for this reaction are kmol/(kg.s.Pa2).
reaction on a 4 wt % Ni0-8 wt % Mo03/HYUS catalyst can be satisfactorily described by a series of parallel and simultaneous reactions including isomerization, cracking, hydrogenolysis, and disproportionation reactions. The kinetic constants of these reactions have been calculated from the initial selectivities for each reaction, obtaining apparent activation energies of 99.1, 169.6,221.4, and 195.9 kJ/mol for the isomerization, hydrogenolysis, cracking, and disproportionation reactions, respectively.
Acknowledgment This work has been supported by the CAICYT, Spain, Project 3699/79.62. Registry No. NiO, 1313-99-1; Moos, 1313-27-5; heptane, 142-82-5;methane, 74-82-8; propane, 74-98-6; isobutane, 75-28-5; butane, 106-97-8; butene, 25167-67-3; isopentane, 7878-4; pentane, 109-66-0; 2-methylpentane, 107-83-5; 3-methylpentane, 96-14-0; hexane, 110-54-3; 2-methylhexane, 591-76-4; 3-methylhexane, 589-34-4; ethane, 74-84-0; pentene, 25377-72-4.
Literature Cited 575
625
675
723
TEMPERATURE ( K )
Figure 3. Temperature dependence of initial conversion. (0) Isomerization, (0)cracking, ( 0 )total conversion.
procedure as well as the validity of the network of the reaction proposed. The values of the apparent activation energies and frequency factors calculated by fitting the rate constants to an Arrhenius-type law are given in Table VI. I t can be observed that the apparent activation energy obtained for the cracking reaction is higher than that obtained by other investigators using bifunctional catalysts similar to that used in the present study. Ribeiro et al. (1982) studied the n-hexane hydrocracking reaction using a Pt/HYUS catalyst, and they calculated an apparent activation energy for the cracking reaction of 146 kJ/mol. Steijns and Froment (1981) have obtained apparent activation energies for the cracking reaction of 138.9 and 149.8 kJ/mol studying the n-decane and n-dodecane hydrocracking reactions, respectively, on a 0.5 wt % Pt/HYUS catalyst. The value obtained by Baltanas et al. (1983) for n-octane cracking with the same catalyst was 136.8 kJ/mol. On the other hand, it must be pointed out that in the first work mentioned the apparent activation energy calculated for the isomerization reaction was 155 kJ/mol, that is to say, a value greater than that obtained for the cracking reaction, while in the other mentioned works the apparent activation energies obtained for both reactions were the same. These results do not concur with those obtained in the present study (see Table VI). In order to justify our results, the variation of the initial conversion (conversion value extrapolated to time on stream equal to zero) of the isomerization, cracking, and overall reactions versus the temperature was obtained from the apparent activation energies given in Table VI and the overall conversion for experiments at constant W / F P This variation can be seen in Figure 3. The shape of these curves is similar to those obtained by other authors studying the hydrocracking reaction on different bifunctional catalysts (Schulz and Weitkamp, 1972; Jacobs et al., 1980; Weitkamp, 1982). This fact seems to confirm the validity of the network of the reaction proposed as well as the values of the apparent activation energies obtained. In conclusion, it can be said that the product distribution obtained experimentally in the n-heptane hydrocracking
Absil, R. P. L.; Butt, J. B.; Dranoff, J. S. "Kinetics of Reaction and Deactivation: Cumene Disproportionation on a Commercial Hydrocracking Catalyst". J . Catal. 1984, 85, 415-427. Baltanas, M. A.; Vansina, H.; Froment, G. F. "Hydroisomerization and Hydrocracking. 5. Kinetic Analysis of Rate Data for nOctane". Ind. Eng. Chem. Prod. Res. Dev. 1983, 22, 531-539. Best, D.; Wojciechowski, B. W. "On Identifying the Primary and Secondary Products of the Catalytic Cracking of Cumene". J . Catal. 1977, 47, 11-27. Bolton, A. P.; Bujalski, R. L. "Role of the Proton in the Catalytic Cracking of Hexane Using a Zeolite Catalyst". J.Catal. 1971,23, 331-339. Corma, A.; M o n t h , J. B.; Orchill&, A. V. "Influence of Acid Strength Distribution on the Cracking Selectivity of Zeolite Y Catalysts". Ind. Eng. Chem. Prod. Res. Dev. 1984, 23, 404-409. Guisnet, M.; Avendano, F.; Bearez, C.; Chevalier, F. "Evidence that Butane Disproportionation Demands Adjacent Acid Sites". J . Chem. Commun. 1985,6, 336-337. Jacobs, P. A.; Uytterhoeven, J. B.; Steijns, M.; Froment, G.; Weitkamp, J. "Hydroisomerization and Hydrocracking. 1. Comparison of the Reactions of n-Decane over Ultrastable Y and ZSM-5 Zeolites containing Platinum". Proc. Int. Conf. Zeolites, 5th 1980, 607-615. Langlois, G . E.; Sullivan, R. F. "Chemistry of Hydrocracking". Ado. Chem. Ser. 1970,97, 38-67. L6pez Agudo, A.; Asensio, A.; Corma, A. "Cracking of n-Heptane on a CrHNaY Zeolite Catalyst. The Network of the Reaction". J. Catal. 1981, 69, 274-282. Ribeiro, F.; Marcilly, C.; Guisnet, M. "Hydroisomerization of nHexane on Platinum Zeolites". J. Catal. 1982, 78, 267-280. Schulz, H. F.; Weitkamp, J. H. 'Zeolite Catalysts. Hydrocracking and Hydroisomerization of n-Dodecane". Ind. Eng. Chem. Prod. Res. Dev. 1972, 11, 46-53. Steijns, M.; Froment, G . F. "Hydroisomerization and Hydrocracking. 3. Kinetic Analysis of Rate Data for n-Decane and n-Dodecane". Ind. Eng. Chem. Prod. Res. Dev. 1981, 20, 660-668. Vizquez, M. I.; Escardino, A.; Aucejo, A.; Corma, A. "Hydrocracking of n-Heptane. Study of NiO-MoOs Catalysts Supported on a HY Ultrastable Zeolite". Can. J. Chem. Eng. 1986, 64,272-277. Vizquez, M. I.; Escardino, A.; Aucejo, A. "Hydrocracking of n-Heptane with a NiO-MoO,/HYUS Zeolite as Catalyst. Kinetic Study". Can. J. Chem. Eng. 1988,66, 313-318. Villermaux, J.; Hoffmann, U.; Kenney, C. N.; Schoon, N. H. "Nomenclature and Symbols Recommended by the Working Party "Chemical Reaction Engineering" of the E.F.Ch.E.". Chem. Eng. Sci. 1980, 35, 2064-2075. Weitkamp, J. "Isomerization of Long-chain n-Alkanes on a Pt/CaY Zeolite Catalyst". Ind. Eng. Chem. Prod. Res. Deu. 1982, 21, 550-558. Yates, D. Y. C.; Taylor, W. F.; Sinfelt, J. H. "Catalysis over Supported Metals. 1. Kinetics of Ethane Hydrogenolysis over Nickel Surfaces of Known Area". J. Am. Chem. SOC.1964,86,2996-3001. Received for review October 20, 1987 Revised manuscript received April 4, 1988 Accepted July 7, 1988
