Recovery of useful lighter fuels from petroleum residual oil by oxidative cracking with steam using iron oxide catalyst

Chemical Engineering Science 65 (2010) 60--65 Contents lists available at ScienceDirect ChemicalEngineeringScience journal homepage: www.elsevier.com/locate/ces Recoveryofusefullighterfuelsfrompetroleumresidualoilbyoxidativecrackingwith steamusingironoxidecatalyst Satoshi Funai, Eri Fumoto, Teruoki Tago, Takao Masuda∗ Division of Chemical System Engineering, Graduate School of Engineering, Hokkaido University, Sapporo 060–8628, Japan A R T I C L E I N F O A B S T R A C T Article history: Received 10 July 2008 Received in revised form 28 February 2009 Accepted 17 March 2009 Available online 26 March 2009 Keywords: Catalytic cracking Iron oxide catalyst Heavy oil Oxidative decomposition Petroleum Residual oil 1. Introduction In petroleum industry, it is desirable to produce lighter hydrocarbons such as gasoline, kerosene and gas–oil from unused heavy oils. Thus we have developed zirconia-supporting iron oxide catalysts (ZrO2–FeOX catalyst) to decompose petroleum residual oil (atmospheric distilled residual oil) with steam. In addition, we have found that the incorporation of Al2O3 among FeOX crystals is effective in improving the catalytic activity and stability of the ZrO2–FeOX catalyst. In this study, the effects of Al2O3 and ZrO2 content in FeOX–based catalysts on catalytic activity and stability were investigated. Furthermore, the FeOX–based catalyst was applied to the decomposition of extra heavy oils such as vacuum distilled resid-ual oil and Orimulsion. These extra heavy oils were effectively decomposed over the ZrO2–Al2O3–FeOX catalyst with steam, and the yields of lighter hydrocarbon reached to above 60% © 2009 Elsevier Ltd. All rights reserved. Matsumura et al. (2005) has reported that the formation of carbon residues can be inhibited under high hydrogen pressures. However, Recently, the demand for useful fuels such as gasoline and kerosene has grown every year. According to the BP Statistical Re-view of World Energy, approximatery half of the primitive petroleum deposits have already been consumed. Therefore, new techniques to produce fuels from unused heavy oils such as atomospheric—or vacuum—distilled residual oils, oil sand, and Orinoco tar are re-quired. Especially, the deposit of oil sand and Orinoco tar is larger than that of the petroleum. Upgrading method for heavy oils by thermal cracking (Zhang et al., 2007), hydrocracking and catalytic cracking (Ali et al., 2002; Dehkissia et al., 2004; Matsumura et al., 2005) have been reported. In these methods, the deposition of carbon residue on the reactor and catalysts was serious problem. Moreover, heavy metals such as vanadium and nickel are contained in heavy oil are usually catalyst poison, leading to catalyst deactivation during reaction. Accordingly, catalysts and/or chemical processes with resistance to heavy metals are required to produce lighter fuels from heavy oil without coke deposition. Several methods have been proposed to overcome these problems. Cho et al. (2001) reported catalyst with resistance to the deposition of heavy metals and a regen-eration method for the deactivated catalyst has been developed. ∗ Corresponding author. Tel./fax: +81117066551. E-mail addresses: takao@eng.hokudai.ac.jp, tago@eng.hokudai.ac.jp (T. Masuda). 0009-2509/$-see front matter © 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.ces.2009.03.028 the hydrogen, which is produced by the reforming of petroleum, is valuable and expensive. We have developed iron oxide (abbreviated FeOX) supporting zir-conia (ZrO2) catalysts (ZrO2–FeOX catalyst), and succeeded in pro-duction of lighter fuels from atomospheric–distilled residual oil (AR) by catalytic cracking in a steam atmosphere (Masuda et al., 1997, 1998, 2001). The active sites to decompose AR are lattice oxygen in FeOX. Since the lattice oxygen is consumed during the reaction, the FeOX-based catalyst without ZrO2 is easily deactivated, which is ob-served in the change in crystallinity of FeOX from hematite to mag-netite. However, because ZrO2 exhibits activity to produce active oxygen species from H2O (Fumoto et al. 2004), the defects of oxygen in FeOX can be supplied by the active oxygen species. Oxidative de-composition occurs in the ZrO2–FeOX catalysts without any carbon residue, so that the FeOX-based catalysts exhibited the high yield of useful lighter hydrocarbons. Moreover, we have reported that an embedded Al2O3 among FeOX crystals is effective for the decrease in domain size of FeOX in FeOX-based catalysts, and the resistance to sintering (Fumoto et al., 2006). In this study, the effects of Al2O3 and ZrO2 content in FeOX-based catalysts were investigated in oxidative cracking of atomospheric–distilled residual oil. Furthermore, the FeOX-based catalyst was applied to decompose the vacuum–distilled residual oil (VR) and Orimulsion. Orimulsion is a mixture of Orinoco tar, water, and surfactant. It is difficult to decompose VR and Orimul-sion because they contain larger amounts of heavy components than AR. S. Funai et al. / Chemical Engineering Science 65 (2010) 60--65 61 2. Experimental section 2.1. Preparation and characterization of FeOX-based catalyst All reagents were purchased from Wako Pure Chemical In-dustries (Japan). FeOX-based catalyst was prepared by a copre- cipitation method using aqueous FeCl3 · 6H2O, ZrOCl2 · 8H2O and Al2(SO4)3 · 14–18H2O. The obtained catalysts were treated with steam at 873K for 1h. The compositions of catalysts were as follows: Al2O3 of 0–13.0wt% (ZrO2/Fe2O3 = 0.097) and ZrO2 of 0–21.2wt% (ZrO2/Fe2O3 = 0.082). The catalyst is denoted hereafter as ZrO2(Y)–Al2O3(Z)–FeOX, where Y and Z are the weight percent of supporting ZrO2 and Al2O3, respectively. Moreover, FeOX, Al2O3 and ZrO2 were also prepared by the same method, and used for cat-alysts for comparison. The structures of the catalysts were analyzed by X-ray diffractometer (JDX–8020; JEOL). 2.2. Catalytic cracking of heavy oils with steam Catalytic cracking with steam was carried out in a fixed-bed type reactor for 2h at a reaction temperature of 773K and atmospheric pressure of 1. A scheme of the reactor is shown in Fig. 1. A mixture of steam and nitrogen was introduced into the stainless steel reactor. The flow rates were 72cm3/min steam and 5cm3/min nitrogen. Prior to the reaction, a catalyst was preheated under the N2 and steam flow at the reaction temperature for 1h. The heavy oils of AR, VR and Orimulsion were used as reactants. The elemental compositions of heavy oils are shown in Table 1. The carbon content of AR and VR was above 80wt%. Because the Orimulsion contented surfactant and water to decrease the viscosity of the orinoco tar, the carbon content was approximately 60wt%. These heavy oils were diluted with benzene at 10wt% to reduce the viscosity. All of the catalysts were confirmed in advance to be inactive to benzene (Masuda et al., 1998; Fumoto et al., 2004). The reactant benzene solutions of heavy oil were fed to the reactor with a syringe pump. The time factor W/F was 1.2h, where F is the flow rate of the feedstock and W is the mass flow controller N2 water amount of the catalysts. The liquid and gaseous products were col-lected with an ice trap and gas pack, respectively. The liquid products were analyzed by a liquid chromatograph (CTO-10A; Shimadzu Co. Ltd.). The gaseous products were analyzed by gas chromatographs with thermal conductivity and flame ionization detectors (GS20B; Shimadzu Co. Ltd.) with activated carbon and Porapak Q columns, respectively. The liquid products with a carbon number of below 6 were ignored in the calculation of the production yield, because benzene was used as cutter stock for the liquid chromatograph. The benzene produced by this reaction was also ignored. The error on the mass balance caused by this procedure was found to be below 5% in a preliminary experiment using a feedstock of AR without benzene as a solvent (Fumoto et al., 2004). To examine the catalytic stability, this sequence of reaction was repeated three times on each catalyst. 3. Results and discussions 3.1. Effect of Al2O3 content on catalytic activity and stability To investigate the effect of Al2O3 content in ZrO2–Al2O3–FeOX catalysts, thecatalytic cracking of ARwith steamwas examined using the FeOX-based catalysts with several Al2O3 contents. The carbon yield and gas composition for the 1st sequence of reaction over the ZrO2–Al2O3–FeOX catalysts and Al2O3 are shown in Figs. 2(a) and (b), respectively. The contents of Al2O3 in the ZrO2–Al2O3–FeOX were 0, 5.0, 7.0, and 13wt%, and the weight ratio of ZrO2/Fe2O3 in the catalysts was 0.097. The composition of AR and the experimental result using Al2O3 were also show in Fig. 2 for comparison. The products were classified into four groups: gas, gasoline+kerosene (carbon number of 7–18), gas–oil (19–29, denote as C19–C29) and heavy oil (above 30, denote as C30+). In Al2O3 catalyst, AR was decomposed without generation of CO2. This result indicates that AR cracking occurred on the acid sites of Al2O3, leading to coke formation. In contrast, as show in the Fig. 2, the heavy components containing in the reactant AR were effectively decomposed into lighter hydrocarbons over FeOX-based catalysts. The carbon residue and coke deposition was not observed on the FeOX-based catalysts, and the major gaseous product after the reac-tion using FeOX-based catalysts was CO2. These results indicated that the oxidative cracking occurred on the FeOX-based catalysts. More-over, the yields of lighter hydrocarbons (gasoline+kerosene) were increased and the yield of heavy oil of the carbon number above 30 feedstock thermo couple furnace tape heater purge was decreased with increasing the Al2O3 content up to 7.0wt%. On the other hand, at the Al2O3 content of 13.0wt%, only the gaseous yield was increased as compared with the other catalysts. In order to clarify the effect of Al2O3 content on the catalytic activity, the domain size of FeOX in the catalysts were calculated by Scherrer`s equation from XRD patterns. The XRD pattern of the catalysts prior to and 1st sequence of reaction are shown in Fig. 3. catalyst (fixed bed) gas pack ice+water Fig. 1. Experimental apparatus of the fixed bed flow reactor. Table 1 Elementary composition of heavy oils (benzene free basis). Heavy oil Carbon (wt%) Nitrogen (wt%) Sulfur (wt%) Others (wt%) AR 84.1 2.1 2.0 11.8 VR 84.4 2.0 3.9 9.7 Orimulsion 60.1 1.2 2.5 36.2 The main peaks of Al2O3 and ZrO2 were also shown in Fig. 3 for comparison. As shown in the Figure, the peaks which attribute to Al2O3 and ZrO2 were not observed, indicating that the crystal sizes of Al2O3 and ZrO2 were too small to be detected. Moreover, be-cause the diffraction peaks of Al2O3 and ZrO2 could not be observed in the catalysts at high Al2O3 and ZrO2 content, it is considered that Al2O3–FeOX and ZrO2–FeOX solid solution were formed. Fig. 4 shows the effect of Al2O3 content on the FeOX domain size of the catalysts prior to reaction. The FeOx domain size decreased with increasing the Al2O3 contents, and exhibited the minimum value around 7.0wt%, and re–increased at Al2O3 content of 13.0wt%. Be-cause Al2O3 was embedded among FeOX crystals (Fumoto et al., 2006), the sintering of FeOX crystals were inhibited, leading to the decrease in FeOX domain size. Accordingly, the increase in the yields of lighter hydrocarbons shown in Fig. 2 resulted from the small do- main size at the Al2O3 content of 7.0wt%. On the other hand, at the 62 S. Funai et al. / Chemical Engineering Science 65 (2010) 60--65 AR C30+ ZrO2 Al2O3 Al2O3 0 wt% C19-C29 5.0 wt% hematite (Fe2O3) ZrO2-Al2O3(0)-FeOx Prior to reaction 7.0 wt% gas 13.0 wt% After 1st sequence ZrO2-Al2O3(5.0)-FeOx Prior to reaction Al2O3 coke gasoline+ After 1st sequence kerosene 0 20 40 60 80 100 Carbon yield / mol% ZrO2-Al2O3(7.0)-FeOx Prior to reaction Al2O3 0 wt% 5.0 wt% 7.0 wt% CH4 others H2 After 1st sequence ZrO2-Al2O3(13.0)-FeOx Prior to reaction After 1st sequence 13.0 wt% CO2 20 magnetite (Fe3O4) 40 60 80 2 h / deg Al2O3 alkene alkane Fig. 3. XRD patterns of the catalysts prior to and after 1st sequence of reaction with the ZrO2–Al2O3(Z)–FeOX. Reaction conditions: T = 873K. 0 20 40 60 80 100 Gas composition / mol% Fig. 2. (a) Carbon yield and (b) gas composition after 1st sequence of the reaction of AR with steam over ZrO2–Al2O3(Z)–FeOX catalysts. Reaction conditions: T = 773K, W/F = 1.2h, P = 0.1MPa. Al2O3 content of 13.0wt%, because the addition of excessive Al2O3 led to the aggregation of Al2O3, the domain size was re–increased. It is considered that the increase in the yields of gas and lighter hy-drocarbons at Al2O3 content of 13.0wt% results from the acid sites of the excessive Al2O3. However, there was no large difference in gas composition between catalyst containing 7.0wt% of Al2O3 and 13.0wt% of Al2O3. This result is ascribed to the composition of cat-alysts. Because the main component in the ZrO2–Al2O3(7.0)–FeOX and ZrO2–Al2O3(13.0)–FeOX was FeOX, the oxidative decomposition of AR mainly occurred over FeOX. Therefore, the product gas com- position in ZrO2–Al2O3(7.0)–FeOX catalyst was similar to that in ZrO2–Al2O3(13.0)–FeOX catalyst. Moreover, after 2nd and 3rd se-quence of reaction, coke deposition was observed on the catalyst at Al2O3 content of 13.0wt%, which is ascribed to the cracking of AR on the acid sited of excessive Al2O3. After the reactions, because the crystal states of FeOX in ZrO2–Al2O3(0)–FeOX and ZrO2–Al2O3(13.0)–FeOX were changed from hematite to magnetite, it was difficult to calculate the domain sizes of the FeOX after reactions. On the contrary, because that of the FeOX in ZrO2–Al2O3(5.0)–FeOX and ZrO2–Al2O3(7.0)–FeOX were unchanged after the reactions, the changes in the FeOX do-main size during the reaction sequence were examined by using these catalysts. The FeOX domain sizes in these catalysts after each reaction are shown in Fig. 5. The domain sizes in these catalysts were almost unchanged after 2nd reaction sequence, whereas in ZrO2–Al2O3(7.0)–FeOX, the domain size slightly decreased after S. Funai et al. / Chemical Engineering Science 65 (2010) 60--65 63 60 30 40 20 20 10 0 0 5 10 Al2O3 content / wt% 0 15 0 1 2 3 4 Sequence of reaction time Fig. 4. The relationship between Al2O3 content and FeOX domain size of the ZrO2–Al2O3(Z)–FeOX catalyst prior to 1st reaction. 3rd reaction sequence. The decrease in the domain size of FeOx in ZrO2–Al2O3(7.0)–FeOX is ascribed to the slight reduction of FeOx from hematite to magnetite, which could not be detected by X-ray diffraction. From a point of view of the catalytic activity and the FeOX domain size, we decided that the adequate Al2O3 content was 7.0wt%. 3.2. Effect of ZrO2 content on catalytic activity and stability To investigate the effect of ZrO2 in ZrO2–Al2O3–FeOX catalysts, the catalytic cracking of AR was examined with the catalysts of sev- eral ZrO2 contents. The carbon yield and gaseous composition after the 1st sequence of reaction over the ZrO2–Al2O3–FeOX catalysts and ZrO2 catalyst are shown in Figs. 6(a) and (b), respectively. The ZrO2 contents in the ZrO2–Al2O3–FeOX catalysts were 0, 8.3, 15.3, 21.2wt%. The weight ratio Al2O3/Fe2O3 in the catalysts was 0.082 (Al2O3 content was 7.0wt%). The composition of AR and the exper-imental result using ZrO2 catalyst are also show in Figs. 6 for com-parison. The gaseous yield was increased as the ZrO2 content increased, and the major composition was CO2. The yields of lighter hydrocar-bons also increased with increasing the ZrO2 contents. In the oxida-tive cracking of AR over FeOX catalyst, the lattice oxygen in FeOX is the active site to decompose AR. The lattice oxygen was consumed during the reaction, which are supplied by active oxygen species generated from H2O over ZrO2 (Fumoto et al., 2004). Accordingly, it was considered that the ZrO2 loading on FeOX enhanced the oxida-tive decomposition of AR. To investigate the effect of ZrO2 content on the crystallinity and FeOx domain size, X-ray diffraction analysis was carried out. The XRD patterns of ZrO2–Al2O3–FeOX catalysts prior to and after the reaction, and the domain size of FeOX prior to the reaction are show in Figs. 7 and 8, respectively. The main peaks of Al2O3 and ZrO2 also were shown in Fig. 7 for comparison. As shown in the figure, the peaks which attribute to Al2O3 and ZrO2 were not observed. The crystallinity of the catalyst without ZrO2(ZrO2(0)–Al2O3–FeOX) transformed from hematite to magnetite after 1st sequence of reac- tion, indicating that FeOX was reduced to magnetite due to the con-sumption of lattice oxygen during the reaction. On the other hand, in ZrO2 content of 8.3wt%, the crystallinity of FeOX-based catalysts was unchanged prior to and after the reaction. 40 30 20 10 0 0 1 2 3 4 Sequence of reaction time Fig. 5. The domain sizes of FeOX in (a) ZrO2–Al2O3(5.0)–FeOX and (b) ZrO2–Al2O3(7.0)–FeOX after each reaction. When the ZrO2 content were above 15.3wt%, however, the crys-tallinity of FeOX was transformed from hematite to magnetite af-ter 1st sequence of reaction. This result is ascribed to the excessive oxidation of AR to produce CO2. The increase in ZrO2 content en-hanced the ability to supply active oxygen species. However, in ZrO2(15.3)–Al2O3–FeOX catalyst, it is considered that the reaction frequency of the lattice oxygen to decompose AR (consumption rate of the lattice oxygen) was higher than the supply rate of the active oxygen species from water. Accordingly, the crystallinity of FeOX was transformed from hematite to magnetite at high ZrO2 content due to the excessive consumption of the lattice oxygen. Moreover, as shown in Fig. 8, the domain size of FeOX was increased with in-creasing the ZrO2 contents, leading to decrease in the surface area of the FeOX-based catalysts. Therefore, from a point of view of cat- alytic stability, including the domain size of FeOX, we decided that the ZrO2(8.3)–Al2O3–FeOX catalyst was appropriate. 3.3. Cracking of VR and Orimulsion over ZrO2(8.3)–Al2O3(7.0)–FeOX with steam Fromthediscussionmentionedabove,ZrO2(8.3)–Al2O3(7.0)–FeOX is an appropriate catalyst to decompose AR without catalyst 64 S. Funai et al. / Chemical Engineering Science 65 (2010) 60--65 ZrO2 AR C30+ Al2O3 ZrO2 0 wt% C19-C29 8.3 wt% hematite (Fe2O3) ZrO2(0)-Al2O3-FeOx Prior to reaction 15.3 wt% 21.2 wt% ... - tailieumienphi.vn