Ind. Eng. Chem. Res. 1989, 28, 139-146
139
Fundamental Hydrodenitrogenation Studies of Polycyclic N-Containing Compounds Found in Heavy Oils. 1. 5,6-Benzoquinoline Joseph Shabtai,* Gene J. C. Yeh, Chris Russell, and Alex G. Oblad Department of Fuels Engineering, University of Utah, Salt Lake City, Utah 84112
T h e hydrodenitrogenation reactions of 5,6-benzoquinoline (1), a component of heavy oils, were systematically investigated as a function of reaction time, temperature, sulfided catalyst type, and CSz (HzS) concentration in the reactant solution. Kinetic rate constants and activation energies were determined for each step of a complex reaction network, which comprises fast hydrogenation of the pyridine ring in 1 (k,) t o yield 1,2,3,4-tetrahydro-5,6-benzoquinoline (2), followed by two competing reactions, i.e., slow C-N hydrogenolysis (k2)versus fast ring hydrogenation (k3)of 2 t o (3a), respectively. yield l-propylnaphthalene (5) and 1,2,3,4,7,8,9,10-octahydro-5,6-benzoquinoline The intermediate compound 3a likewise undergoes competing C-N hydrogenolysis (It5) versus further (4a) and perhydro-5,6ring hydrogenation (126) to yield l-propy1-1,2,3,4-tetrahydronaphthalene benzoquinoline (6); respectively. Under the experimental conditions (temperature, 79-330 "C; Hz pressure, 2500 psig; sulfided CoMo and NiMo catalysts), k3 >> kZ,while It5 > k6, indicating t h a t (aromatic) C-N bond hydrogenolysis is much slower, whereas (aliphatic) C-N bond hydrogenolysis is faster, as compared with competing ring hydrogenation. Activation energies (kilocalories/mole) determined were 12.4 for hydrogenation of a conjugated pyridine ring, 12.7 for a conjugated benzene ring, and 39.4 for a nonconjugated (single) benzene ring; 24.4 for (aliphatic) C-N bond hydrogenolysis, and 49.4 for (aromatic) C-N bond hydrogenolysis. T h e high Hz consumption in the overall HDN process underlines the need for improved sulfided catalysts, possessing augmented C-N hydrogenolysis versus ring hydrogenation selectivity. It was reported recently that hydrodenitrogenation (HDN) of heavy oils in the presence of sulfided NiMo, NiW, and CoMo catalysts proceeds with very high hydrogen consumption, e.g., 8-11 mol of H2 per g-atom of N removed (Shabtai et al., 1988~). The large number of previous HDN studies notwithstanding, these results would indicate the necessity of a deeper insight in the chemistry, kinetics, and catalysis of HDN processes, preferably through studies of realistic model compounds, e.g., N-containing polycyclics found as components of heavy oils. This in turn could provide the basis for the design of new HDN catalysts possessing augmented C-N bond hydrogenolysis versus ring hydrogenation selectivity (Shabtai et al., 1988a), and lead to higher HDN efficiency in heavy oil hydroprocessing. It has been indicated that nitrogen in heavy petroleum fractions and in synfuels is mostly in the form of condensed aromatic-N-heterocyclic compounds (Smith, 1968; Katti et al., 1986). Previous model HDN studies have been performed mainly with bicyclic compounds, e.g., quinoline and indole, as feeds, although some studies with tricyclic compounds, e.g., acridine, have also been reported. The HDN of such compounds was found to involve ring hydrogenation, followed by C-N bond hydrogenolysis. Thus, the HDN of indole proceeds with initial hydrogenation of the pyrrole ring, followed preferentially by hydrogenation of the adjacent benzene ring prior to N removal (Liu et al., 1984; Stern, 1979; Rollman, 1977). Likewise, HDN of quinoline has been found to involve preferential hydrogenation of the pyridine moiety followed by hydrogenation of the adjacent benzene ring prior to C-N hydrogenolysis (Shih et al., 1977; Miller and Hineman, 1984; Satterfield and Cocchetto, 1981; Satterfield and Gultekin, 1981; Satterfield and Yang, 1984). For acridine, the HDN process was similarly found to proceed mainly via complete hydrogenation of the condensed ring system prior to hydrogenolytic N removal (Bhinde et al., 1979). It was found recently that the C-N hydrogenolysis versus ring hydrogenation selectivity of Mo-based hydrotreating catalysts depends strongly on the composition of 0888-5885/89/2628-0139$01.50/0
the catalyst and, in particular, on the nature of the transition-metal promoter (Shabtai et al., 1988a). Catalyst activity and selectivity were found to depend also on the method of presulfiding (Yang and Satterfield, 1983) and on the level of H,S addition during the HDN process (Yang and Satterfield, 1984; Satterfield and Gultekin, 1981). Thus, it was found in the latter studies that addition of H2S enhanced the C-N hydrogenolysis activity but depressed the ring hydrogenation activity of a NiMo/y-Al,O, catalyst. It was also reported that oxygen-containing compounds inhibited the HDN of indole (Odebunmi and Ollis, 1983a,b),whereas sulfur-containing feeds inhibited the HDN of pyridine a t e325 "C but enhanced the HDN rate for the same feed at temperatures >325 "C (Satterfield et al., 1975). Kinetic data obtained in several HDN studies of pure model compounds, e.g., indole (Stern, 1979),quinoline (Shih et al., 1977; Satterfield and Yang, 1984), and acridine (Bhinde et al., 19791, have been found to fit pseudo-first-order kinetics. In other studies, however, authors have proposed Langmuir-Hinshelwood rate expressions, based on strong adsorption of the N-heterocyclic substrates, and consequent self-inhibition of the HDN reactions and deviations from first-order kinetics (Satterfield and Cocchetto, 1981; Miller and Hineman, 1984). In a relevant HDN kinetics study of quinoline, it was found that the denitrogenation reaction follows pseudo-first-order kinetics at low nitrogen concentrations but deviates and shows non-first-order kinetics a t high nitrogen concentration in the feed (Miller and Hineman, 1984). Systematic HDN studies of a variety of tricyclic and tetracyclic compounds, found in heavy oils, were undertaken in this laboratory. Condensed ring systems containing pyridine or pyrrole rings in either end or middle positions, and situated in various steric environments, were investigated. The present first paper of a series reports a systematic study of the HDN reactions of 5,6-benzoquinoline as a function of reaction time and temperature, sulfided catalyst type, and H2S concentration in the reaction mixture. 0 1989 American Chemical Society
140 Ind. Eng. Chem. Res., Vol. 28, No. 2, 1989 Table I. Mass Spectral Data on Products from Hydrogenation-HDN of 5,6-Benzoquinoline (1) molecular product (no.)" peak, M l e major fragmentation peaks, m / e b 182 (81), 167 (27), 154 (20), 128 (131, 91 (9), 77 (14) 183 1,2,3,4-tetrahydr0-5,6-B$(2) 186 (40), 158 (23), 144 (35), 129 (55), 128 (43), 115 (47), 56 (42) 187 1,2,3,4,7,8,9,10-octahydro-5,6-BQ (3a) 186 (66), 159 (58), 158 (34), 144 (29), 130 (18),115 (lo), 77 (15) 187 1,2,3,4,11,12,13,14-octahydro-5,6-BQ (3b) 131 (loo), 116 (7), 115 (101,91 (171, 77 (4) 174 l-n-propyl-1,2,3,4-tetrahydro-N (4a) 145 (loo), 131 (871, 129 (20), 115 (19), 91 (201, 77 (11) 174 5-n-propyl-1,2,3,4-tetrahydro-N (4b) 1-n-propyl-N ( 5 ) 170 142 (12), 141 (loo), 128, 115 1-n-propyldecahydro-N (7) 180 137 (go), 95 (70), 81 (loo), 71 (141, 69 (33), 67 (57), 57 (321, 55 (49) trans isomer 137 (49), 95 (70), 81 (loo), 71 (211, 69 (321, 67 (84), 57 (60), 55 (65) 180 cis isomer 192 (19), 122 (loo), 96 (50), 83 (21), 82 (16), 70 (23), 57 (35), 56 (24), 55 (19) 193 perhydro-5,6-BQ (6)c a BQ = benzoquinone; N = naphthalene. bRelative intensities given in parentheses. given are the strongest observed.
Experimental Section Catalysts. CoMo and NiMo catalysts supported on 7-A1203were prepared by incipient wetness impregnation, using the following sequential procedure. The support (Ketjen 7-A1203; 20-40 mesh; surface area, 209 m2/g; pore volume, 0.6 cm3/g) was calcined a t 540 "C for 16 h and then impregnated with an aqueous solution of (NH,),Mo7OZ4.The impregnated sample was oven-dried a t 120 "C for 16 h and then impregnated with an aqueous solution of C O ( N O ~or) ~Ni(N03). The resulting, sequentially impregnated catalyst was dried at 120 "C overnight and then calcined in air at 540 "C for 16 h. Catalysts containing 3% or 6% Co (or Ni) and 8% Mo were prepared. A catalyst, designated as (step)3CoSMo, was prepared by stepwise impregnation of the Mo/y-A1203 precursor with the Co(NO& solution, using three consecutive steps. Following each impregnation step (using each time one-third of the total amount of Co promoter), the catalyst was dried at 120 "C and then calcined at 540 "C. A catalyst, designated as Oa5F3Co8Mo,was prepared by impregnation of a finished 3Co8Mo catalyst with the calculated amount of an aqueous NH4HF2solution, followed by drying at 120 "C and calcination at 540 "C. Prior to their use, all catalysts were presulfided at 380 "C for 4 h under a stream of 10% H2S-90% H2 (40 cm3/min). Apparatus a n d Experimental Procedure. Experiments were performed in a specially designed Magnedash autoclave, provided with a high-temperature sampling device. In each run were used 0.5 g of 5,6-benzoquinoline dissolved in 100 cm3 of n-dodecane, and 2 g of catalyst. CS2 (0.09 g) was added to the feed in order to maintain the sulfided state of the catalyst during the experiment. In kinetic runs, the feed, catalyst, and CS2 were charged to the autoclave, and the latter was closed and then purged consecutively with nitrogen and hydrogen. The reactor was pressurized with hydrogen to 1000 psig and heated quickly to the reaction temperature without stirring. The stirrer was turned on, and the system was quickly brought to the desired reaction pressure (2500 psig). This point was taken as the zero reaction time. Depending on the reaction temperature, samples were withdrawn every 10, 20, or 30 min and analyzed with a Varian 3700 gas chromatograph, equipped with FID and nitrogen-sensitive (TSD) detectors. The volume of each sample was measured, and the H2 pressure in the system was held constant at 2500 psig by addition of hydrogen through a regulator and a check valve. At the end of each run, the reactor was cooled down to room temperature, and the residual liquid product was removed and its volume measured. A fast dashing rate (250 dashes/min) was provided during the experiment to ensure that the reaction is not interparticle diffusion controlled (increase in dashing rate does not affect the conversion). Catalysts with a particle
Consisting of at least three stereoisomers; intensities
R E T E N T I O N TIME, MlN
Figure 1. Gas chromatographic separation of products from hydrogenation-HDN of 5,6-benzoquinoline (column, 6% OV 17; detectors, FID and TSD; heat-up rate, 4 'C/min from 120 to 270 "C).
size in the range 20-40 mesh were employed, in order to prevent any significant intraparticle diffusion resistance. Although the HDN reaction is exothermic, heat effects were negligible since a very dilute reactant solution ( IrMo > CrMo > PtMo > CoMo > FeMo > NiMo > ReMo > RhMo > PdMo. The high selectivity of the RuMo, IrMo, and PtMo catalysts is due to a favorable balance of moderate C-N hydrogenolysis activity and very low ring hydrogenation activity. HDN reactions with such catalysts could be expected to proceed with lower hydrogen consumption, as compared with conventional NiMo and CoMo catalysts. Further work on the testing and optimization of Mo-based catalysts with promoters, e.g., Ru, Ir and Pt (and possibly Cr), alone or in combination with promoters having high C-N hydrogenolysis activity, in particular Ni, would be essential for development of improved sulfided catalysts for hydroprocessing of heavy oils. Acknowledgment The financial support of the US Department of Energy (Contract DE-AC22-79E514700) is gratefully acknowledged. Registry No. 1 , 85-02-9; 2 , 40174-35-4; 3, 61100-87-6; 4, 66324-83-2; 5, 2765-18-6; 6 , 117897-86-6; CO, 7440-48-4; Mo, 7439-98-7; Ni, 7440-02-0.
Literature Cited Benson, S. W. Thermochemical Kinetics; Wiley: New York, 1976. Bhinde, M. V.; Shih, S.; Zawadsky, R.; Katzer, J. R.; Kwart, H. Hyrodenitrogenation over Molybdenum-Containing Catalysts. Proc. 3rd Internat. Confer. on Chemistry and Uses of Molybdenum, Climax, 1979; p 184. Himmelblau, D. M.; Jones, C. R.; Bischoff, K. B. Fundamentals 1967, 6 ( 4 ) ,539. Katti, S. S.; Gates, B. C.; Petrakis, L. Catalytic Hydroprocessing of SRC-I1 Heavy Distillate Fractions. 6. Ind. Eng. Chem. Process Des. Deu. 1986, 25, 618. Liu, Y.; Massoth, F. E.; Shabtai, J. Catalytic Functionalities of Supported Sulfides. 111. Bull. SOC.Chim. Belg. 1984, 93, 627. Miller, J. T.; Hineman, M. F. Non-First-Order Hydrodenitrogenation Kinetics of Quinoline. J . Catal. 1984, 85, 117. Odebunmi, E. 0.;Ollis, D. F. Catalytic Hydrodeoxygenation. 11. J . Catal. 1983a, 80, 65.
Odebunmi, E. 0.;Ollis, D. F. Catalytic Hydrodeoxygenation. 111. J. Catal. 1983b, 80, 76. Rollmann, L. D. Catalytic Hydrogenation of Model Nitrogen, Sulfur, and Oxygen Compounds. J. Catal. 1977,46, 243. Satterfield, C. N.; Cocchetto, J. F. Reaction Network and Kinetics of the Vapor Phase Hydrodenitrogenation of Quinoline. Ind. Eng. Chem. Process Des. Dev. 1981, 20, 53. Satterfield, C. N.; Gultekin, S. Effect of Hydrogen Sulfide on the Catalytic Hydrodenitrogenation of Quinoline. Ind. Eng. Chem. Process Des. Deu. 1981, 20, 62. 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. Deu. 1984,23,11. Satterfield, C. N.; Modell, M.; Mayer, J. F. Interactions Between Catalytic Hydrodesulfurization of Thiophene and Hydrodenitrogenation of Pyridine. AIChE J. 1975,21, 1100. Shabtai, J.; Guohe, Q.; Balusami, K.; Nag, N. K.; Massoth, F. E. Catalytic Functionalities of Supported Sulfides. V. C-N Bond Hvdrogenolvsis Selectivity as a Function of Promoter TvDe. _ _ J. Cata1.-1988a, 113, 206. Shabtai. J.: Nag. N. K.: Massoth. F. E. Catalvtic Functionalities of Supported culfides. IV. C - 0 Hydrogenolsyis Selectivity as a Function of Promoter Type. J. Catal. 1987, 104, 413. Shabtai, J.; Nag, N. K.; Massoth, F. E. Proc. 9 t h Internat. Congr. Catalysis; Calgary, M. J., Phillips, M., Ternan, Eds.; The Chemical Institute of Canada: Ottawa, 1988b; Vol. 1 , pp 1-10. Shabtai, J.; Yeh, G. J. C.; Russell, C.; Oblad, A. G. Kinetics of Hydrodenitrogenation of SRC-I1 Liquids and Synfuel-Simulating Blends. Fuel 1988c, 67, 314. Shih, S. S.; Katzer, J. R.; Kwart, H.; Stiles, A. B. Quinoline Hydrodenitrogenation: Reaction Network and Kinetics. Prepr.-Am. Chem. SOC.,Diu. Pet. Chem. 1977,22(3),919. Smith, H. M. Qualitative and Quantitative Aspects of Crude Oil Composition. US Department of the Interior, Bureau of Mines, Washington, DC, 1968, pp 21-22. Stern, E. W. Reaction Networks in Catalytic Hydrodenitrogenation. J. Catal. 1979, 57, 390. Yang, S. H.; Satterfield, C. N. Some Effects of Sulfiding a NiMo/ A1,0, Catalyst on its Activity for Hydrodenitrogenation of Quinoline. J. Catal. 1983, 81, 168. Yang, S. H.; Satterfield, C. N. Catalytic Hydrodenitrogenation of Quinoline in a Trickle-Bed Reactor. Effect of Hydrogen Sulfide. Ind. Eng. Chem. Process Des. Deu. 1984, 23, 20. Received for review June 15, 1988 Accepted November 9 , 1988
Preparation and Characterization of a Plate-Supported Raney Copper Catalyst J o r g e Laine,* Gustavo Ceballos, and F r a n c i s c o Severino Laboratorio d e Catdlisis HeterogBnea, Centro d e Qulmica, Instituto Venezolano d e Investigaciones Cientificas, Apartado 21827, Caracas 1020-A, Venezuela
Germfin C a s t r o Grupo d e Fisica d e Superficies, Uniuersidad Central de Venezuela, Apartado 21201, Caracas 1020-A, Venezuela
A method for the preparation of a Raney copper catalyst in the form of a film deposited on a stainless steel plate has been devised. Heat treatment was found to be necessary in order to create a proper linking between the precursor alloy film and the plate. The alloy film consisted of A12Cu grains of about 10-20 pm dispersed over an alloy groundfilm. The structure of grains was also seen in the Raney copper, resulting after leaching with NaOH solution. Surface area of the Raney film was significantly higher than those obtained when preparing common Raney copper catalysts. The activity for CO oxidation of the Raney film was of the same order as those obtained when using either bulk Raney copper or copper on alumina catalysts. Ceramic porous materials are widely used as support for catalysts. However, these types of supports offer two major problems: one is their poor strength against attrition
* To whom
correspondence should be addressed.
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phenomena and the other is their low thermal conductivity that promotes the appearance of undesirable "hot points" when operating under highly exothermic reaction conditions. Typical ceramic-based catalysts are in the form of pellets, which may create undesirable pressure buildup in 0 1989 American Chemical Society
