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Energy & Fuels 2009, 23, 1338–1341
Recovery of Lighter Fuels by Cracking Heavy Oil with Zirconia-Alumina-Iron Oxide Catalysts in a Steam Atmosphere† Eri Fumoto,* Akimitsu Matsumura, Shinya Sato, and Toshimasa Takanohashi Energy Technology Research Institute, National Institute of AdVanced Industrial Science and Technology, 16-1 Onogawa, Tsukuba 305-8569, Japan ReceiVed August 1, 2008. ReVised Manuscript ReceiVed December 23, 2008
This paper describes catalytic cracking, with zirconia-supporting iron oxide catalysts in a steam atmosphere, of heavy oil, such as petroleum residual oil, to recover as much lighter fuel as possible. In this process, the heavy oil reacts with active oxygen species generated from steam over the iron oxide catalyst and significant amounts of lighter fractions and carbon dioxide are produced with almost no coke. Active hydrogen species generated from steam are added to the heavy and middle fractions, producing gasoline, kerosene, and gas oil (boiling points less than 350 °C). Large amounts of these lighter fuels (48 mol % C) were produced by the catalytic cracking of residual oil, which contained 93 mol % C of heavy oil fraction (boiling points above 350 °C), with a zirconia-alumina-iron oxide catalyst at 500 °C, with lesser amounts (20 mol % C) at 450 °C. More alumina was mixed to the catalyst to promote the cracking of heavy oil at lower temperatures. This modified catalyst was found to be better for cracking heavy oil, even at 450 °C, and the total amount of lighter fuels was as large as that obtained at 500 °C.
1. Introduction Greater quantities of lighter fuels, such as gasoline, kerosene, and gas oil, are required, although the petroleum reserves of the world are limited. There are huge amounts of atmosphericand vacuum-distilled residual oil in the petroleum-refining process that could be converted into valuable lighter fuels. Thermal cracking,1,2 catalytic cracking,3,4 and hydrocracking5-7 are the conventional methods for producing lighter fuels from residual oil. However, large quantities of coke are formed in reactors and on catalysts when using these methods, and this leads to the plugging of the reactors and rapid deactivation of the catalysts. It is necessary to crack residual oils at a high hydrogen pressure to reduce this coke formation; however, this process is expensive. Fumoto et al. have investigated the cracking of residual oils with steam as an alternative hydrogen source. In the previous papers, both atmospheric and vacuum residual oils were successfully cracked with zirconia-supporting iron oxide catalysts in a steam atmosphere.8-10 These residual oils were † Presented at the 9th International Conference on Petroleum Phase Behavior and Fouling. * To whom correspondence should be addressed. E-mail:
[email protected]. (1) Wang, J.; Anthony, E. J. Chem. Eng. Sci. 2003, 58, 157–162. (2) Bi, W.; McCaffrey, W. C.; Gray, M. R. Energy Fuels 2007, 21, 1205–1211. (3) Cho, S. I.; Jung, K. S.; Woo, S. I. Appl. Catal., B 2001, 33, 249– 261. (4) Jolodar, A. J.; Akbarnejad, M. M.; Taghizadeh, M.; Marvast, M. A. Chem. Eng. J. 2005, 108, 109–115. (5) Ancheyta, J.; Betancourt, G.; Marroquı´n, G.; Centeno, G.; Castan˜eda, L. C.; Alonso, F.; Mun˜oz, J. A.; Go´mez, Ma. T.; Rayo, P. Appl. Catal., A 2002, 233, 159–170. (6) Dhkissia, S.; Larachi, F.; Chornet, E. Fuel 2004, 83, 1323–1331. (7) Matsumura, A.; Kondo, T.; Sato, S.; Saito, I.; Souza, W. F. Fuel 2005, 84, 411–416. (8) Fumoto, E.; Tago, T.; Tsuji, T.; Masuda, T. Energy Fuels 2004, 18, 1770–1774. (9) Fumoto, E.; Tago, T.; Masuda, T. Energy Fuels 2006, 20, 1–6.
oxidatively decomposed with the catalyst. Active oxygen and hydrogen species were generated from steam over the catalyst. The active oxygen species reacted with the heavy oil fractions to produce lighter fractions and carbon dioxide without any coke, while the active hydrogen species were added to the lighter fractions. However, the zirconia-supporting iron oxide catalyst was deactivated when the reaction and regeneration sequence was repeated. Fumoto et al. reported that the iron oxide changed from hematite into magnetite and the subsequent peeling of zirconia from the catalyst caused the deactivation.9 To reduce this change, alumina was added to the iron oxide lattice and zirconia was highly dispersed in the iron oxide catalyst to produce a zirconia-alumina-iron oxide catalyst. This catalyst exhibited almost the same activity as the original catalyst, and its activity did not change after repeated reactions of residual oil.10 Thus, while Fumoto et al. did succeed in developing a zirconia-alumina-iron oxide catalyst to decompose residual oils in a steam atmosphere, the reaction conditions, such as temperature, were not investigated in sufficient detail. Fumoto et al. had previously investigated the reaction of the residual oils with steam at 500 °C, and conventional hydrocracking are performed below 450 °C. Stainless-steel reactors may be less durable at temperatures above 500 °C. In this work, we investigated the effect of the temperature on the catalytic activity in heavy oil decomposition and the catalyst was greatly improved for producing lighter fuels at lower temperatures. In addition, we examined the effect of steam on the catalytic activity for the decomposition of heavy oil. 2. Experimental Section 2.1. Catalysts and Feedstock. Zirconia-alumina-iron oxide catalysts were prepared by the co-precipitation method by the addition of ammonia to aqueous solutions containing iron(III) (10) Fumoto, E.; Tago, T.; Masuda, T. Chem. Lett. 2006, 35, 998–999.
10.1021/ef8006257 CCC: $40.75 2009 American Chemical Society Published on Web 01/22/2009
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Table 1. Properties of AR Derived from Middle East Crude density (g/cm3) C (wt %) H (wt %) N (wt %) S (wt %) H/C CCRa (wt %) V (ppm) Ni (ppm) Fe (ppm) a
0.944 85.7 11.6 0.16 2.48 1.63 5.8 10 4 10
Conradson carbon residue.
Figure 2. Distillation curves of liquid product after the reaction of AR with the Zr-Al(7.0)-FeOx catalyst in a steam atmosphere. Reaction conditions: T ) 450-550 °C, W/F ) 1.4 h, and FS/F ) 3.2 g/g.
Figure 1. Experimental apparatus for the catalytic cracking of heavy oil.
chloride, aluminum sulfate, and zirconium oxychloride (concentrations of FeCl3 · 6H2O ) 120-140 mol/m3, Al2(SO4)3 · 14-18H2O ) 9.0-20 mol/m3, and ZrOCl2 · 8H2O ) 7.3-8.7 mol/m3). The catalyst was treated with steam at 600 °C for 1 h. The catalysts produced in this manner are referred to as Zr-Al(Y)-FeOx catalysts, where Y is the amount of alumina by weight percent. The ratio of zirconia to iron oxide was 1:10 by weight. Al2O3 and ZrO2-Al2O3 catalysts were also prepared by the co-precipitation method and calcinated at 600 °C for 1 h followed by steam treatment for 1 h at the same temperature. The zirconia content in the ZrO2-Al2O3 catalyst was about 30 wt %. These catalysts were pelletized without any binders, crushed, and sieved to yield particles 250-560 µm in diameter, which were used in further experiments. The structure of the catalysts was analyzed using an X-ray diffractometer (XRD, M03XHF22, Mac Science Co. Ltd., Japan). We used atmospheric-distilled residual oil (AR) derived from Middle East crude in this study. Table 1 shows the properties of this oil. The AR was diluted with inert solvent to reduce its viscosity. Toluene was used as the solvent because a preliminary experiment confirmed that the activity of the catalyst to decompose toluene was negligible. The toluene solution containing 10 wt % of AR was used as a feedstock. 2.2. Catalytic Cracking. We used a fixed-bed reactor to conduct catalytic cracking of AR with steam, as shown in Figure 1. Approximately 1.5 g of the Zr-Al(Y)-FeOx catalyst was loaded into the rector, and the AR-toluene solution was introduced using a syringe pump. The reaction took place at a temperature of 450-550 °C under atmospheric pressure. The time factor W/F was 1.4 h, where F is the flow rate of the feedstock and W is the amount of the catalyst. A mixture of steam and nitrogen was introduced into the reactor as a carrier gas at a flow rate of 0-4.4 × 10-3 m3/h steam and 3.0 × 10-4 m3/h nitrogen. The ratio of steam to feedstock, FS/F, was 0-3.2 by weight, where FS is the flow rate of the steam. The products and the used catalysts were analyzed after the reaction of AR for 2 h. AR experiments with Al2O3 and ZrO2-Al2O3 catalysts were conducted using the same procedure. The spent catalyst was calcined at 600 °C in an air stream after treatment at 600 °C in a nitrogen atmosphere using a thermogravimeter (TG, TGA-50, Shimadzu Co. Ltd., Japan), and the
weight of coke was measured. The liquid and gas products were separated in an ice trap. The gas product collected in a sampling bag was quantitatively analyzed by gas chromatographs with a thermal conductivity detector (GC-12A, Shimadzu Co. Ltd., Japan) equipped with Porapak-Q and a flame ionization detector (GC-14A, Shimadzu Co. Ltd., Japan) equipped with Unibeads 3S columns. The yields of coke and gas products collected were determined by TG and GC analyses, and the rest was assumed to be the liquid product. The boiling range distribution of the liquid product was analyzed by a gas chromatographic distillation apparatus (GC-17A, Shimadzu Co. Ltd., Japan) equipped with an automatic injector and a wide-bore capillary column. The samples contained toluene, which was used as the solvent to reduce the viscosity of the AR. The boiling range distribution was calculated after the peak of toluene was omitted. Namely, the compounds with a lower boiling point than toluene were omitted. The error in the mass balance caused by this procedure was found to be less than 5% in a preliminary experiment.8
3. Results and Discussion 3.1. Effect of the Reaction Temperature on the Yield of Lighter Fuels by Catalytic Cracking of AR. Figure 2 shows typical distillation curves of liquid products with the Zr-Al(7.0)-FeOx catalyst when the reaction was carried out at 450, 475, 500, and 550 °C. The feedstock curve is shown for comparison. The curves of the liquid products at each temperature were shifted to the right compared to those of the feedstock, indicating that the products contained lower boiling components than the feedstock. The amount of lower boiling components increased with the temperature; the liquid product at 500 °C contained the largest amount of lower boiling components. To determine the yield of lighter fuels, these liquid products were defined as three fractions, gasoline + kerosene (boiling point less than 250 °C), gas oil (boiling point of 250-350 °C), and heavy oil (boiling point of 350-600 °C). Figure 3 shows the product yield and gas composition after the reaction with the Zr-Al(7.0)-FeOx catalyst. The composition of AR is shown for comparison. The heavy oil fraction was decomposed over the catalyst, producing lighter fuels, such as gasoline, kerosene, and gas oil. In particular, significant amounts of lighter fuels were recovered at 475-500 °C without any coke. The main gas product of the reaction was carbon dioxide. Masuda et al. reported that the active oxygen and hydrogen species were generated from steam over the zirconia-supporitng iron oxide catalyst.11 Therefore, it was indicated that these active species (11) Masuda, T.; Kondo, Y.; Niwa, M.; Shimotori, T.; Mukai, S. R.; Hashimoto, K.; Takano, M.; Kawasaki, S.; Yoshida, S. Chem. Eng. Sci. 2001, 56, 897–904.
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Figure 3. Effect of the reaction temperature on the (a) product yield and (b) gas composition after the reaction of AR with the Zr-Al(7.0)-FeOx catalyst in a steam atmosphere. Reaction conditions: T ) 450-550 °C, W/F ) 1.4 h, and FS/F ) 3.2 g/g.
were generated from steam over the catalyst in this reaction.9 The heavy oil was oxidatively cracked with the active oxygen species over the catalyst, and lighter fractions and carbon dioxide were generated without any coke, while the active hydrogen species were added to the lighter fractions. This resulted in significant amounts of lighter fuels. At 550 °C, the gas yield increased and some coke was formed. It appears that heavy oil was cracked rapidly at 550 °C and the active species might not be generated from steam in sufficient quantity. This resulted in the formation of coke. As shown in Figure 3, the total yield of lighter fuels at 450 °C was considerably lower than that at 500 °C. The cracking reaction of heavy oil on the Zr-Al(7.0)-FeOx catalyst may not occur so readily at 450 °C, although active hydrogen and oxygen species were generated from steam. 3.2. Modification of the Zirconia-Alumina-Iron Oxide Catalyst. To promote the cracking of heavy oil at lower temperatures, we prepared a modified catalysts containing more alumina (13.0-16.6 wt %). Figure 4 shows the effect of different catalysts at 450 °C. The yield of the heavy oil fraction decreased with an increasing alumina content, and the largest amounts of gasoline, kerosene, and gas oil were generated with the Zr-Al(16.6)-FeOx catalyst. Thus, this modified catalyst with a greater alumina content must have promoted the cracking of heavy oil. To examine the activity of the alumina in decomposing heavy oil, we conducted catalytic cracking of AR with Al2O3 and ZrO2-Al2O3 catalysts. The results are shown in Figure 5. Heavy oil fractions were cracked with both catalysts, and lighter fuels and some coke were generated. The main gas products were olefin and methane, although carbon dioxide was the main product with the Zr-Al(Y)-FeOx catalyst, as shown in Figure 4b. It is known that alumina and zirconia have the acidic and basic properties. Accordingly, heavy oil fractions were decomposed over the alumina and zirconia, yielding lighter fractions
Fumoto et al.
Figure 4. (a) Product yield and (b) gas composition after the reaction of AR with Zr-Al(Y)-FeOx catalysts at 450 °C in a steam atmosphere. Reaction conditions: W/F ) 1.4 h and FS/F ) 3.2 g/g.
Figure 5. (a) Product yield and (b) gas composition after the reaction of AR with Al2O3 or ZrO2-Al2O3 catalysts at 450 °C in a steam atmosphere. Reaction conditions: W/F ) 1.4 h and FS/F ) 3.2 g/g.
and coke. The results of the reaction with the Al2O3 and ZrO2-Al2O3 catalysts indicate that the alumina contained in the Zr-Al(Y)-FeOx catalyst promoted the cracking of heavy oil. Thus, heavy oil fractions were cracked over the iron oxide and alumina, and the cracked fractions reacted with the active oxygen and hydrogen species generated from steam over the iron oxide catalyst. Zirconia is known to promote the generation
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Figure 6. Effect of the steam flow rate on the product yield after the reaction of AR with the Zr-Al(7.0)-FeOx catalyst. Reaction conditions: T ) 500 °C, W/F ) 1.4 h, and FS/F ) 0-3.2 g/g.
of these active species from steam.8 Therefore, heavy oil fractions were effectively cracked with the Zr-Al(16.6)-FeOx catalyst, even at 450 °C in a steam atmosphere, without producing any coke. 3.3. Effect of Steam on the Catalytic Activity to Convert AR into Lighter Fuels. The effect of the steam flow rate on the product yield was investigated using the Zr-Al(7.0)-FeOx catalyst. The time factor W/F was fixed to be a constant residence time of feed when the steam flow rate was changed. Figure 6 shows the product yield at 500 °C. The yield of lighter fuels, such as gasoline, kerosene, and gas oil, was independent of the steam flow rate, indicating that heavy oil fractions were effectively cracked over the catalyst. However, some coke was formed on the catalyst after the reaction at lower steam flow rates. This suggests that large amounts of active oxygen and hydrogen species were generated at high steam concentrations, and the heavy oil fraction then reacted with these species to yield lighter fractions without any coke. At lower steam flow rates, insufficient generation of these species may have been the cause of the coke formation. When the reaction was conducted without steam, the heavy oil reacted with the lattice oxygen in the iron oxide catalyst and lighter fractions and carbon dioxide were generated. The heavy oil fractions were almost not decomposed at all in the reaction without a catalyst. These results suggest that the lattice oxygen in the iron oxide catalyst reacted with the heavy oil fractions. 3.4. X-ray Diffraction Analysis of the Zr-Al(7.0)FeOx Catalyst. Figure 7 shows XRD patterns of the Zr-Al(7.0)-FeOx catalyst prior to and after the reaction with AR. The catalyst prior to the reaction exhibited a hematite structure. The structure of the catalyst changed very little after the reaction at 500 °C with the higher steam flow rate (FS/F ) 3.2). In the previous work, the catalytic activity to decompose heavy oil was durable after the reaction of AR at 500 °C for 4 h.10 Accordingly, it was supposed that the catalytic performance did not change during the reaction for 4 h in the higher steam flow rate. When catalytic cracking was conducted at 500 °C with the lower steam flow rate (FS/F ) 1.0) and without any steam at all, the hematite structure of the catalyst changed to magnetite. Heavy oil fractions were cracked over the catalyst, while the fractions were almost not decomposed in the reaction without catalyst (Figure 6). These results indicate that heavy oil fractions reacted with lattice oxygen in the iron oxide catalyst. Because large amounts of the active oxygen species were mainly generated over the zirconia from the steam at high steam concentrations, these species were available to the iron oxide lattice; therefore, the hematite structure did not change. The active oxygen species in the catalyst reacted with heavy oil fractions, yielding lighter fractions without any coke. On
Figure 7. XRD pattern of the Zr-Al(7.0)-FeOx catalyst prior to and after the reaction of AR. Reaction conditions: T ) 500-550 °C, W/F ) 1.4 h, and FS/F ) 0-3.2 g/g.
the other hand, incorporation of these species into the iron oxide lattice was insufficient at lower rates of steam because of the production of fewer oxygen species; this caused the structure to change from hematite into magnetite. Thus, some heavy oil fractions did not react with active oxygen species and produced some coke. Lattice oxygen in the iron oxide was completely consumed during the reaction without steam because no active oxygen species were generated. As a result, the hematite structure changed into magnetite and coke formed. The structure of the catalyst changed from hematite to magnetite after the reaction with steam (FS/F ) 3.2) at 550 °C. This indicates that heavy oil fractions reacted rapidly with the lattice oxygen in the iron oxide, yielding lighter fractions and carbon dioxide; the active oxygen species were not supplied to the iron oxide lattice in sufficient quantity. Consequently, some heavy oil fractions did not react with these species over the catalyst, and some coke was formed. 4. Conclusion Catalytic cracking of AR with the Zr-Al(Y)-FeOx catalyst was conducted at 450-550 °C in a steam atmosphere. Heavy oil was oxidatively cracked over the Zr-Al(7.0)-FeOx catalyst. The largest amount of lighter fuels, such as gasoline, kerosene, and gas oil (boiling points less than 350 °C), was generated without any coke at 500 °C. In this reaction, heavy oil reacted with lattice oxygen in the iron oxide and the active oxygen species generated from the steam were incorporated into the iron oxide lattice. Therefore, the heavy oil reacted with these species over the iron oxide catalyst to yield lighter fuels, and the active hydrogen species generated from steam were added to the lighter fuels. However, the amount of lighter fuels generated at 450 °C was considerably lower than that at 500 °C. A Zr-Al(16.6)-FeOx catalyst that contains more alumina was developed to promote the cracking of heavy oil at lower temperatures. We found that this modified catalyst was more suitable for producing lighter fuels at 450 °C. Alumina in the catalyst promotes the cracking of heavy oil, and oxidative cracking of heavy oil occurs preferably over the iron oxide catalyst. Acknowledgment. The authors acknowledge the financial support of the Japan Petroleum Energy Center. EF8006257
