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Transfer hydrocracking of heavy oils with metal-supported carbon catalyst
T. Inui et al. (Editors), New Aspects of Spillover Effect in Catalysis 0 1993 Elsevier Science Publishers B.V. All rights reserved.
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Transfer hydrocracking of heavy oils with metal-supported carbon catalyst Ikusei Nakamura, Kohjiro Aimoto and Kaoru Fujimoto Department of Synthetic Chemistry, Faculty of Engineering, The University of Tokyo 7-3-1, Hongo, Bunkyo-ku, Tokyo, 113 Japan
Abstract Liquid phase hydrocracking of Kuwait atmospheric residue which was conducted in the presence of metal-supported active carbon gave large amount of distillates (70%) with small or no hydrogen consumption. The yield of asphaltene in the product oil was very low, whereas coke yield was relatively high (about lOwt%). In the metal-free active carbon system, coke yield and content of olefins, sulfur compounds and asphaltene in the product oil increased, and 38 m3/kl-oil of hydrogen was formed. These results suggested that asphaltene in the feed oil was adsorbed on the metal supported active carbon catalyst and was decomposed on it to form coke and hydrogen atoms. The hydrogen atoms formed migrated on the carbon surface to reach the metal site and transferred to free radicals or olefins. 1. INTRODUCTION Upgrading of heavy oils such as residual oil or oil-sand bitumen to distillates is one of the most important technologies of next generation energy development. Hydrocracking is a promising technology which makes high quality kerosene and gas oil [ l l . However, it consumes large quantity of hydrogen(330-400 Nm3/kl-oil). In the present work, new method for upgrading heavy oils to produce high quality middle distillates with small hydrogen consumption, namely transfer hydrocracking, was developed and the role of catalyst was clarified.
2. EXPERIMENTAL Catalysts were prepared by impregnating active carbon and the other variety of carrier materials with nickel nitrate and other water soluble metal salts. The catalyst precursor was dried in air at 120 "C, calcined in flowing nitrogen at 450 "C for 3h and activated by reduction flowing hydrogen at 450 "C for 3h and then sulfided with a H,-H,S mixed gas (4/1 mole ratio) at 400 "C for 1 h. Kuwait atmospheric residue (KW-AR) was cracked using an autoclave with inner volume of 150 ml and apparatus to make hydrogen gas flow. Reaction conditions were as follows: feed oil, 40g; catalyst, 8-12 g; hydrogen pressure, 0-7.5 MPa; reaction temperature, 435-455 OC; process time, 30-60 min; and out let gas flow rate, 120 ml/min.
362
Gaseous products were analyzed by using gas chromatographs. Liquid products were distilled to naphtha(1BP-171 "C), kerosene(172-232 "C), gas oil(233-343 "C) and residue(343 OC+ fraction). The contents of paraffins, olefins and aromatic hydrocarbons were determined by FIA method. The amount of coke, asphaltene and maltene were determined as toluene insoluble, toluene soluble-pentane insoluble and pentane soluble, respectively. Maltene was analyzed by silica-alumina column chromatographs for saturates (SA), monoaromatics (MA), diaromatics (DA), triaromatics (TA) and polyaromatics and polar compounds (PP).
3. RESULTS AND DISCUSSION 3.1. Product patterns of catalyzed and non-catalyzed reaction
The results of KW-AR cracking with various supported Ni catalyst and without catalyst are given in Figure 1. Carrier materials were commercially available active carbon, (3"-A1,0,
which is a typical basic support and SO,-Al,O,, which is a typical acidic support. The characteristics of the Ni/A.C. catalyzed reaction are summarized as follows: (1)The yield of gaseous hydrocarbon was lower than that of noncatalyzed or Si0,-A1 0, catalyzed reaction, whereas the conversion of KW-AR were similar for these reactions. ($)The content of olefins in the distillates was very low, although the hydrogen consumption for Ni/A.C. system and Ni/P"AI,O, system was in the same level. (3)The coke yield was highest in these systems but the yield of asphaltene was almost zero. a) H, consumption Sa; Saturates, MA; Monoaromatics, DA; Diaromatics. TA; Triaromatics, PP; Polyaromatics and polar compounds, As; Asphaltene, AR-KW 40 g, Catalyst 8g, Reaction temp. 435 "C, Hydrogen pres. 7.5 MPa. Process time 60 min.
Figure 1. Product patterns of KW-AR cracking
363
These results suggest that the asphaltene in the residual oil was adsorbed on or decomposed on the catalyst surface and was then converted to coke in the case of the carbon-catalyzed reaction. At the same time olefins were hydrogenated to paraffins.
3.2. Effects of supported metals on active carbon In table 1 are shown the result of KW-AR cracking at 455 O C over a variety of sulfided metal catalyst supported on a commercially available active carbon. Conversion level was promoted from 67 % to 80 % or higher by adding active carbon catalysts whether it carried metals or not. The increase in the conversion level should be attributed to catalytic action of active carbon, since the free radical on active carbon surface should initiate cracking reaction. In the metal-free active carbon system, coke yield and content of sulfur compounds and olefins in product oil were higher than that of the metal supported active carbon systems, except for lwt% of supported iron catalyst. Table 1 Effects of supported metals on active carbon Cat a 1ys t
Noncat. A.C.
Nilwt% A.C.
Molwt% A.C.
79.3
85.6 17.7 53 62.4
Felwt% A.C.
FelOwtB A.C.
~~
Conversion (wt%) 67.3 Coke yield (wt%) 6.6 H, consumption (Nm3/kl) - 3 4 Sulfur removal (wt%) 15.2
87.3 21.1 -38 22.6
14.9 67
60.0
88.0 21.9 -24 29.7
83.9 7.5 73
64.1
~~
Composition of Naphtha Paraffins ( ~ 0 1 % ) Olef ins ( ~ 0 1 % ) Aromatics ( ~ 0 1 % )
72 10 18
83
90
9
0 10
8
KW-AR 40 g, catalyst 12 g, temp. 455 'C,
3.3. Effects of hydrogen pressure
88 2 10
76 7 17
92 1 7
time 3 0 min, H, press. 7.5 MPa
The effects of hydrogen pressure on the Ni/A.C.-catalyzed reaction of KW-AR are shown in Figure 2. With increasing hydrogen pressure, hydrogen consumption increased linearly and conversion of residual oil decreased slightly. Also, the degree of desulfurization increased and coke yield decreased with the increase in hydrogen pressure up to 3.0 m a , but they were almost constant over 3.0 MPa. Since the degrees of desulfurization and the coke yield are considered a measure of the hydrogenation of product oil, it is reasonable that the hydrogenation of product oil reached the same level in the case of 3.8 and 7.5 MPa of hydrogen pressure. The fact that hydrogenation of product oil was at the same level for reaction at hydrogen pressure of 3.8 and 7.5 MPa, while the hydrogen consumption at 3.8 MPa was much lower than that at 7.5 MPa, suggests that gaseous hydrogen is mainly consumed in the hydrogenation of the products at 7.5 MPa. On the other hand, when the hydrogen pressure was low, the dehydrogenation of asphaltene to coke was enhanced and the hydrogen atom on the catalyst, which was formed from asphaltene coking, reacted with sulfur compounds or oil without desorbing to gas phase.
364
10
30
6 4
l A
0
2.0
6.0 8.0 H, pressure (MPa) 4.0
0
Figure 2. Effects of hydrogen pressure. KW-AR 40g, Ni 1wt%/A.C. 8g, 435 OC, 60 min.
Figure 3. Reaction model of hydrogen transfer cracking.
3.4. Reaction model of the present system and role of catalyst The reaction model of the present system is demonstrated as in Figure 3. In the system, most of the heavy oil is cracked thermally in the liquid phase to produce free radicals, olefins and smaller paraffins. On the other hand, the asphaltene which usually contains poly-cyclic moieties, is adsorbed and cracked or dehydrogenated on the surface of active carbon, probably because of the chemical affinity between the aromatic nuclei of asphaltene and carbon surface and the dehydrogenating activity of active carbon surface, to form coke and hydrogen atoms. The hydrogen atoms on the carbon surface migrate on it to reach supported metal particles, where, they react with olefins, free radicals or sulfur compounds or they recombine to hydrogen molecules to be desorbed into gas phase. When the reaction is operated under pressurized hydrogen, hydrogen molecules are adsorbed on metal surface to dissociate to hydrogen atoms, whereby the desorption of hydrogen from the carrier surface is suppressed. This phenomenon is called spillover effect [2]. When the pressure of hydrogen in the gas phase is high, hydrogen in the gas phase comes into the metal surface to react with other materials resulting the hydrogen consumption. When the hydrogen pressure is low. the hydrogen on the solid surface should be desorbed to gas phase by the reverse spillover 131. Under particular hydrogen pressure, neither absorption nor desorption of hydrogen would be observed as demonstrated in Figure 2. 4. REFERENCES 1 R.B. Agnihitri, L.G. Bourgeois, J.E. Crosby and M.D. Hamman, Hydrocarabon Proce.,
June (1987) 47. 2 K. Fujimoto, S. Toyoshi and T. Kunugi, Procs. 7th Inter. Conf. on Catalysis, (1981) 235. 3 K. Fujimoto, A. On0 and T. Kunugi, Stud. in Surf. Sci. and Cat., 17 (1983) 241.
36 1
Transfer hydrocracking of heavy oils with metal-supported carbon catalyst Ikusei Nakamura, Kohjiro Aimoto and Kaoru Fujimoto Department of Synthetic Chemistry, Faculty of Engineering, The University of Tokyo 7-3-1, Hongo, Bunkyo-ku, Tokyo, 113 Japan
Abstract Liquid phase hydrocracking of Kuwait atmospheric residue which was conducted in the presence of metal-supported active carbon gave large amount of distillates (70%) with small or no hydrogen consumption. The yield of asphaltene in the product oil was very low, whereas coke yield was relatively high (about lOwt%). In the metal-free active carbon system, coke yield and content of olefins, sulfur compounds and asphaltene in the product oil increased, and 38 m3/kl-oil of hydrogen was formed. These results suggested that asphaltene in the feed oil was adsorbed on the metal supported active carbon catalyst and was decomposed on it to form coke and hydrogen atoms. The hydrogen atoms formed migrated on the carbon surface to reach the metal site and transferred to free radicals or olefins. 1. INTRODUCTION Upgrading of heavy oils such as residual oil or oil-sand bitumen to distillates is one of the most important technologies of next generation energy development. Hydrocracking is a promising technology which makes high quality kerosene and gas oil [ l l . However, it consumes large quantity of hydrogen(330-400 Nm3/kl-oil). In the present work, new method for upgrading heavy oils to produce high quality middle distillates with small hydrogen consumption, namely transfer hydrocracking, was developed and the role of catalyst was clarified.
2. EXPERIMENTAL Catalysts were prepared by impregnating active carbon and the other variety of carrier materials with nickel nitrate and other water soluble metal salts. The catalyst precursor was dried in air at 120 "C, calcined in flowing nitrogen at 450 "C for 3h and activated by reduction flowing hydrogen at 450 "C for 3h and then sulfided with a H,-H,S mixed gas (4/1 mole ratio) at 400 "C for 1 h. Kuwait atmospheric residue (KW-AR) was cracked using an autoclave with inner volume of 150 ml and apparatus to make hydrogen gas flow. Reaction conditions were as follows: feed oil, 40g; catalyst, 8-12 g; hydrogen pressure, 0-7.5 MPa; reaction temperature, 435-455 OC; process time, 30-60 min; and out let gas flow rate, 120 ml/min.
362
Gaseous products were analyzed by using gas chromatographs. Liquid products were distilled to naphtha(1BP-171 "C), kerosene(172-232 "C), gas oil(233-343 "C) and residue(343 OC+ fraction). The contents of paraffins, olefins and aromatic hydrocarbons were determined by FIA method. The amount of coke, asphaltene and maltene were determined as toluene insoluble, toluene soluble-pentane insoluble and pentane soluble, respectively. Maltene was analyzed by silica-alumina column chromatographs for saturates (SA), monoaromatics (MA), diaromatics (DA), triaromatics (TA) and polyaromatics and polar compounds (PP).
3. RESULTS AND DISCUSSION 3.1. Product patterns of catalyzed and non-catalyzed reaction
The results of KW-AR cracking with various supported Ni catalyst and without catalyst are given in Figure 1. Carrier materials were commercially available active carbon, (3"-A1,0,
which is a typical basic support and SO,-Al,O,, which is a typical acidic support. The characteristics of the Ni/A.C. catalyzed reaction are summarized as follows: (1)The yield of gaseous hydrocarbon was lower than that of noncatalyzed or Si0,-A1 0, catalyzed reaction, whereas the conversion of KW-AR were similar for these reactions. ($)The content of olefins in the distillates was very low, although the hydrogen consumption for Ni/A.C. system and Ni/P"AI,O, system was in the same level. (3)The coke yield was highest in these systems but the yield of asphaltene was almost zero. a) H, consumption Sa; Saturates, MA; Monoaromatics, DA; Diaromatics. TA; Triaromatics, PP; Polyaromatics and polar compounds, As; Asphaltene, AR-KW 40 g, Catalyst 8g, Reaction temp. 435 "C, Hydrogen pres. 7.5 MPa. Process time 60 min.
Figure 1. Product patterns of KW-AR cracking
363
These results suggest that the asphaltene in the residual oil was adsorbed on or decomposed on the catalyst surface and was then converted to coke in the case of the carbon-catalyzed reaction. At the same time olefins were hydrogenated to paraffins.
3.2. Effects of supported metals on active carbon In table 1 are shown the result of KW-AR cracking at 455 O C over a variety of sulfided metal catalyst supported on a commercially available active carbon. Conversion level was promoted from 67 % to 80 % or higher by adding active carbon catalysts whether it carried metals or not. The increase in the conversion level should be attributed to catalytic action of active carbon, since the free radical on active carbon surface should initiate cracking reaction. In the metal-free active carbon system, coke yield and content of sulfur compounds and olefins in product oil were higher than that of the metal supported active carbon systems, except for lwt% of supported iron catalyst. Table 1 Effects of supported metals on active carbon Cat a 1ys t
Noncat. A.C.
Nilwt% A.C.
Molwt% A.C.
79.3
85.6 17.7 53 62.4
Felwt% A.C.
FelOwtB A.C.
~~
Conversion (wt%) 67.3 Coke yield (wt%) 6.6 H, consumption (Nm3/kl) - 3 4 Sulfur removal (wt%) 15.2
87.3 21.1 -38 22.6
14.9 67
60.0
88.0 21.9 -24 29.7
83.9 7.5 73
64.1
~~
Composition of Naphtha Paraffins ( ~ 0 1 % ) Olef ins ( ~ 0 1 % ) Aromatics ( ~ 0 1 % )
72 10 18
83
90
9
0 10
8
KW-AR 40 g, catalyst 12 g, temp. 455 'C,
3.3. Effects of hydrogen pressure
88 2 10
76 7 17
92 1 7
time 3 0 min, H, press. 7.5 MPa
The effects of hydrogen pressure on the Ni/A.C.-catalyzed reaction of KW-AR are shown in Figure 2. With increasing hydrogen pressure, hydrogen consumption increased linearly and conversion of residual oil decreased slightly. Also, the degree of desulfurization increased and coke yield decreased with the increase in hydrogen pressure up to 3.0 m a , but they were almost constant over 3.0 MPa. Since the degrees of desulfurization and the coke yield are considered a measure of the hydrogenation of product oil, it is reasonable that the hydrogenation of product oil reached the same level in the case of 3.8 and 7.5 MPa of hydrogen pressure. The fact that hydrogenation of product oil was at the same level for reaction at hydrogen pressure of 3.8 and 7.5 MPa, while the hydrogen consumption at 3.8 MPa was much lower than that at 7.5 MPa, suggests that gaseous hydrogen is mainly consumed in the hydrogenation of the products at 7.5 MPa. On the other hand, when the hydrogen pressure was low, the dehydrogenation of asphaltene to coke was enhanced and the hydrogen atom on the catalyst, which was formed from asphaltene coking, reacted with sulfur compounds or oil without desorbing to gas phase.
364
10
30
6 4
l A
0
2.0
6.0 8.0 H, pressure (MPa) 4.0
0
Figure 2. Effects of hydrogen pressure. KW-AR 40g, Ni 1wt%/A.C. 8g, 435 OC, 60 min.
Figure 3. Reaction model of hydrogen transfer cracking.
3.4. Reaction model of the present system and role of catalyst The reaction model of the present system is demonstrated as in Figure 3. In the system, most of the heavy oil is cracked thermally in the liquid phase to produce free radicals, olefins and smaller paraffins. On the other hand, the asphaltene which usually contains poly-cyclic moieties, is adsorbed and cracked or dehydrogenated on the surface of active carbon, probably because of the chemical affinity between the aromatic nuclei of asphaltene and carbon surface and the dehydrogenating activity of active carbon surface, to form coke and hydrogen atoms. The hydrogen atoms on the carbon surface migrate on it to reach supported metal particles, where, they react with olefins, free radicals or sulfur compounds or they recombine to hydrogen molecules to be desorbed into gas phase. When the reaction is operated under pressurized hydrogen, hydrogen molecules are adsorbed on metal surface to dissociate to hydrogen atoms, whereby the desorption of hydrogen from the carrier surface is suppressed. This phenomenon is called spillover effect [2]. When the pressure of hydrogen in the gas phase is high, hydrogen in the gas phase comes into the metal surface to react with other materials resulting the hydrogen consumption. When the hydrogen pressure is low. the hydrogen on the solid surface should be desorbed to gas phase by the reverse spillover 131. Under particular hydrogen pressure, neither absorption nor desorption of hydrogen would be observed as demonstrated in Figure 2. 4. REFERENCES 1 R.B. Agnihitri, L.G. Bourgeois, J.E. Crosby and M.D. Hamman, Hydrocarabon Proce.,
June (1987) 47. 2 K. Fujimoto, S. Toyoshi and T. Kunugi, Procs. 7th Inter. Conf. on Catalysis, (1981) 235. 3 K. Fujimoto, A. On0 and T. Kunugi, Stud. in Surf. Sci. and Cat., 17 (1983) 241.