Energy Fuels 2010, 24, 4419–4424 Published on Web 07/08/2010
: DOI:10.1021/ef100531u
Catalytic Hydrotreating of the Diesel Distillate from Fushun Shale Oil for the Production of Clean Fuel Hang Yu,*,†,‡ Shuyuan Li,† and Guangzhou Jin§ † State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing 102249, China, ‡CNOOC New Energy Investment Company, Limited, Beijing 100015, China, and §Beijing Institute of Petrochemical Technology, Beijing 102617, China
Received April 27, 2010. Revised Manuscript Received June 21, 2010
Because of high contents of nitrogen, sulfur, and unsaturated hydrocarbons in shale oil, its potential use as a substitute fuel is limited. In this paper, catalytic hydrotreating of the diesel fraction (200-360 °C) from Fushun shale oil was preliminarily investigated in a fixed-bed reactor. Hydrotreating experiments were carried out using various available commercial catalysts, including CoMo/Al2O3, NiW/Al2O3, and NiMoW/Al2O3, at different conditions of temperature, hydrogen pressure, liquid hourly space velocity (LHSV), and ratio of hydrogen/feedstock. The results showed that the NiMoW catalyst was most active for heteroatom removal, in comparison to other catalysts. Under relative mild conditions, it was possible to produce clean diesel from a Fushun shale oil distillate. The produced oil had low contents of sulfur, nitrogen, and alkene, reduced density, and increased cetane number, and it could be used as a more valuable fuel.
a transportation fuel. Denitrogenation was more difficult than desulfurization for shale oils.3-11 Many factors, including feedstock properties, catalyst performance, and processing conditions, can affect the removal of heteroatomic compounds by hydrotreating.12,13 To deepen the heteroatom removal extent and moderate catalytic conditions, the diesel distillate (200-360 °C) from Fushun shale oil was chosen for catalytic hydrotreating in the present paper. Three different types of catalysts were used and compared according to the conversion of nitrogen and sulfur compounds. The effects of processing conditions on the desulfurization and denitrogenation were investigated.
1. Introduction The exploitation and use of energy alternatives have attracted more and more attention in the world because of the gradual decrease of the petroleum reserves. As an unconventional energy, oil shale, a natural organic sedimentary rock, is being used in many countries at present. In China, reserves of oil shales account for about 500 000 billion tons. It is distributed mainly in Fushun, Liaoning province, Huadian, Jilin province, and Maoming, Guangdong province.1,2 There are two conventional ways for the use of oil shale, including burning to generate electricity power and retorting to produce shale oil. However, the shale oils produced from oil shales contain a considerable amount of heteroatomic compounds, especially unsaturated hydrocarbons, which may cause many troubles, such as, instability of fuel during its transportation or storage. In addition, direct combustion of the shale oil will result in emissions of NOx and SOx. Catalytic hydrotreating may be considered as the only convenient way to remove heteroatomic compounds from shale oil. However, many papers showed that severe process conditions were needed during catalytic hydrotreating of shale oils. The concentrations of heteroatomic compounds in shale oils could be reduced, but they were still too high to be used as
2. Experimental Section 2.1. Preparation of Samples. The shale oil used in the present study was obtained from Fushun, China. The diesel distillate was prepared by fractionation of the crude shale oil using the distillation apparatus. (6) Luik, H.; Lindaru, E.; Vink, N.; Maripuu, L. Upgrading of Estonia shale oil distillation fractions. 1. Hydrogenation of the “diesel fraction”. Oil Shale 1999, 16, 141–148. (7) Luik, H.; Vink, N.; Lindaru, E.; Maripuu, L. Upgrading of Estonia shale oil distillation fractions. 2. The effect of time and hydrogen pressure on the yield and composition of “diesel fraction” hydrogenation products. Oil Shale 1999, 16, 249–256. (8) Luik, H.; Maripuu, L.; Vink, N.; Lindaru, E. Upgrading of Estonia shale oil distillation fractions. 3. Hydrogenation of light mazute. Oil Shale 1999, 16, 331–336. (9) Su, Z. S.; Liu, P.; Cai, L.; Zhao, G. F. Hydrotreating of Fushun shale oil. Contemp. Chem. Ind. 2008, 37, 246–248. (10) Zhao, G. F.; Su, Z. S.; Liu, H. Study on diesel production by shale oil hydrocracking. Contemp. Chem. Ind. 2007, 36, 361–366. (11) Yoshida, R.; Miyazawa, M.; Yoshida, T.; Narita, H.; Maekawa, Y. Chemical structure chages in Condor shale oil and catalytic activities during catalytic hydrotreatment. Fuel 1996, 75, 99–102. (12) Song, C. S.; Ma, X. L. New design approaches to ultra-clean diesel fuels by deep desulfurization and deep dearomatization. Appl. Catal., B 2003, 41, 207–238. (13) Landau, M. V. Deep hydrotreating of middle distillates from crude and shale oils. Catal. Today 1997, 36, 393–429.
*To whom correspondence should be addressed. Telephone: 86-1089733287. E-mail:
[email protected]. (1) Jiang, X. M.; Han, X. X.; Cui, Z. G. Progress and recent utilization trends in combustion of chinese oil shale. Prog. Energy Combust. Sci. 2007, 33, 552–579. (2) Qian, J. L.; Yin, L. Shale Oil;Alternative Energy for Petroleum; Sinopec Press: Beijing, China, 2008. (3) Chishti, H. M.; Williams, P. T. Aromatic and hetero-aromatic compositonal changes during catalytic hydrotreatment of shale oil. Fuel 1999, 78, 1805–1815. (4) Williams, P. T.; Chishti, H. M. Reaction of nitrogen and sulphur compounds during catalytic hydrotreatment of shale oil. Fuel 2001, 80, 957–963. (5) Benyamna, A.; Bennouna, C.; Moreau, C.; Geneste, P. Upgrading of distillate fractions of Timahdit Moroccan shale oil over a sulphided NiO-MoO3/γ-Al2O3 catalyst. Fuel 1991, 70, 845–848. r 2010 American Chemical Society
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: DOI:10.1021/ef100531u
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Figure 1. Schematic diagram of the fixed-bed reactor.
measured using a 5 cm3 calibrated glass pycnometer. The alkene contents in oil could be determined by their bromine values measured by a bromine value analyzer. The oils were analyzed by liquid chromatography to separate the oils into chemical class fractions. The liquid chromatography, which consists of a glass column packed with silica (pretreated at 145 °C for 2 h) and alumina (pretreated at 450 °C for 4 h). A diesel distillate of 0.05 g was added to the top of the column. After sequential elution of the column with petroleum ether (30-60 °C), a mixed petroleum ether-dichloromethane solution, and a mixed dichloromethane-methanol solution, the saturated, aromatic, and polar fractions (resin and asphaltene) can be obtained, respectively. For each fraction, after solvents were evaporated completely, the percentage of each fraction was calculated. The oils before and after hydrotreating were analyzed with Agilent 6890N/5973 gas chromatography-mass spectrometry (GC-MS) equipped with a HP-PONA methyl siloxane capillary column (50 m 0.2 mm 0.5 μm). The initial temperature of the column in the GC-MS system was set at 80 °C and held at that temperature for 2 min. Then, the column was heated at a constant heating rate of 2 °C min-1 to the final temperature of 300 °C and held at that temperature for 10 min. Injector and detector temperatures were set at 320 and 280 °C, respectively. Mass spectra were obtained at an electron impact potential of 70 eV with a range of 30-500 amu. Data were acquired and processed using Chemstation software. The organic compounds were identified by comparing mass spectra to National Institute of Standards and Technology (NIST) library data.
Table 1. Composition and Properties of the Catalysts
NiO (wt %) WO3 (wt %) CoO (wt %) MoO3 (wt %) surface area (m2/g) pore volume (mL/g)
CoMo
NiW
NiMoW
3.7 14.5
2.9 28.0
3.2 30.5
180 0.31
160 0.29
2.6 200 0.49
2.2. Hydrotreating Experiments. The experiments on catalytic hydrotreating were carried out in a fixed-bed microreactor unit. The schematic diagram of the microreactor unit was shown in Figure 1. The liquid feed was pumped to the upside of the reactor, mixed with H2, and entered into the reactor. The desired pressure of the reactor was controlled by a pressure-reducing regulator and back-reducing regulator. The desired gas flow was controlled by a mass flow meter. The unit had a cylindrical reactor with an inside diameter of 10 mm and a volume of 35 cm3. Product oil and gas passed through a condensator, after which the liquid product was collected in a container and the gas product was let out through a back-reducing regulator. Three types of catalysts were used in the present study, including NiW/Al2O3, CoMo/Al2O3, and NiMoW/Al2O3. The composition and properties of the catalyst are shown in Table 1. All catalysts were obtained from a petroleum refinery in China. Al2O3 was used as a catalyst carrier. For each test, 6 mL of crushed catalyst (20-40 mesh) was loaded in the isothermal zone of the reactor. The catalysts were presulfided using a solution of 5 wt % CS2 in cyclohexane. The NiW catalyst was presulfided at 360 °C under a hydrogen pressure of 4 MPa, with a liquid hourly space velocity (LHSV) of 3 h-1, feedstock ratio (v/v) of 500, sulfiding time of 4 h. The catalysts CoMo and NiMoW were presulfided for 3 h, while the other conditions were the same. Hydrotreating of this diesel distillate was continuously carried out after presulfiding of the catalyst. After 5 h of continuous operation, the catalyst was stabilized by feeding the diesel distillate under the reaction conditions. Sampling of the hydrotreated oil was started 2 h later after the reaction conditions were changed, to confirm the constant catalytic activity. 2.3. Oil Analysis. The total contents of nitrogen and sulfur in oils were determined by a UV fluorescence sulfur meter and a chemical radiation nitrogen meter, respectively. The density was
3. Results and Discussion Table 2 shows a summary of the properties of the Fushun shale oil. The properties of Fushun shale oil were similar to petroleum oils but contained higher contents of nitrogen and unsaturated hydrocarbons, which resulted in a low hydrogen/ carbon ratio. The elemental analysis of the distillates obtained from Fushun shale oil is shown in Table 3. The diesel distillate (200-360 °C) accouted for about 41.6% of Fushun shale oil. The nitrogen content rose by increasing the boiling point, indicating that most of the nitrogen compounds distribute in a high boiling cut (>360 °C). The sulfur distribution showed a minimum at 200-360 °C. Thus, the diesel distillate 4420
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fraction. However, scission of some kinds of polycyclic aromatic compounds may give an additional amount of aromatic fraction. Whether the aromatic fraction increased or decreased after catalytic hydrotreating depended upon the relative contents of these compounds in the feedstock. In addition, the dramatic decrease in the bromine value in Table 4 suggested that the contents of alkenes were reduced significantly. There was a distinct decrease in the density and an increase in the cetane number resulting from aromatic hydrogenation. The obtained products were more stable than the feedstock. However, they still darkened during storage. Table 4 also showed that the increasing of the temperature and hydrogen pressure was profitable for the heteroatom removal, alkene saturation, and quality improvement of the product. Liang et al.14 stated that the temperature and hydrogen pressure in addition to space velocity and hydrogen/feedstock ratio were the principal operating parameters in catalytic hydotreating of petroleum oils. Williams et al. also showed that a higher pressure produced a derived shale oil with higher hydrogen contents and reduced coke formation on the catalyst together with the reduction of nitrogen and sulfur contents. Zhu et al.15 reported the influence of reaction conditions on heteroatom removal of a high-sulfur-content shale oil. They showed that, as the reaction temperature rose from 300 to 400 °C, the percentage of sulfur removal increased from 57.75 to 98.12%, while nitrogen removal increased from 25.29 to 82.76%. The work reported here also confirmed that a higher temperature and hydrogen pressure produced a derived shale oil with a high cetane number and reduced density together with a reduction of nitrogen and sulfur contents. In Table 5, the NiW catalyst showed better catalytic activity. At the present conditions, the higher percentage of nitrogen removal (from about 35.9 to about 73.8%) was reached. In addition, a little more aromatics were hydrogenated because higher decreases in density and increases in cetane number were obtained. Desulfurization activity of the CoMo catalyst was higher than the NiW catalyst at moderate conditions. For example, the percentage of sulfur removal for the NiW catalyst was 85.9% at 320 °C, 4 MPa, 1 h-1, and 600:1, while it was 88.4% for the CoMo catalyst at the same conditions. However, the difference became comparable at more severe conditions. The percentages of sulfur removal were 96.9 and 96.8% for CoMo and NiW, respectively, at 360 °C, 5 MPa, 1 h-1, and 600:1. The products obtained were still unstable and darkened during storage. In Table 6, the NiMoW catalyst gave better hydrotreating ability for this diesel distillate compared to the previous two catalysts. The percentage of sulfur removal was from 95.6 to 99.2%. The product had a sulfur content of 43 μg g-1 at severe conditions (360 °C, 5 MPa, 1 h-1, and 600:1). Denitrogenation degrees were from 37.9 to 77.6%, which were a little higher than that of the NiW catalyst at severe conditions. Slight decreases in density and bromine value and an increase in the cetane number were found compared to that of the previous two catalysts. In summary, the catalytic activity of desulfurization and denitrogenation in the present work may be ordered as
Table 2. Properties of the Fushun Shale Oil properties
fushun shale oil
density at 20 °C (g/mL) moving viscosity at 50 °C (mm2/s) freezing point (°C) flash point (°C) carbon (wt %) hydrogen (wt %) oxygen (wt %) nitrogen (wt %) sulfur (wt %) hydrogen/carbon ratio characterization factor
0.9033 31.3 33 133 84.19 11.95 1.88 1.27 0.71 1.70 11.52
(200-360 °C) of Fushun shale oil was chosen as the researching object in this paper, to obtain high-quality products at moderate process conditions. Tables 4-6 give experimental results of the diesel distillate investigated and their hydrotreated products at different processing conditions. On the basis of the contents of sulfur and nitrogen in feedstock and products, degrees of sulfur and nitrogen removal over catalysts used were calculated. In Table 4, the CoMo catalyst showed high desulfurization activity. The percentage of sulfur removal ranged from 88.4 to 96.9%, depending upon process conditions. It indicated that most of the sulfur-containing compounds in this distillate were reactive, which can be easily converted during the catalytic hydroprocessing. In contrast to high desulfurization activity, the nitrogen removal over this catalyst was more difficult. Hydrodenitrogenation (HDN) degrees were from 28.0 to 50.3%. Other workers have also shown that sulfur was much more easily removed from shale oil during catalytic hydroprocessing than nitrogen.3-9 It has been suggested that nitrogen removal during catalytic hydrotreating is a two-step process, while sulfur removal is a one-step process. Both nitrogen and sulfur are found to occur mostly as aromatic compounds. HDN is believed to require complete hydrogenation of aromatic rings because C-N bonds are much stronger in an aromatic ring than the naphthenic structure. In contrast, the removal of sulfur dos not require the complete saturation of the aromatic ring containing sulfur but involves direct scission of the C-S bond. Table 4 also showed the chemical class fractionations of the feedstock and after catalytic hydrotreating in relation to process conditions for the CoMo catalyst. Catalytic hydrotreating produced a marked decrease in the polar fraction, from 29.0 wt % in the feedstock rising to 10.6 wt % at the most severe condition, which can be attributed to the removal of heteroatom compounds. Similarly, the aromatic fraction decreased from 13.1 to 10.5 wt % in the product. However, these results were inconsistent with some researchers. For example, Yoshida et al.11 used the NiMo catalyst to hydrotreat the heavy distillate (73%, boiling point > 325 °C) of Comdor shale oil at 22-23 MPa and 400 and 450 °C in relation to the reaction time of up to 120 min. They reported that aromatic contents of the hydrotrated oils were increased as the hydrotreating time was increased. Also, Willams et al.4 catalytically hydrotreated shale oil with the NiMo catalyst at 15.0 MPa and 400 °C in a stirred reactor and residence time from 8 to 56 h. They found that, after hydrotreating, there was a marked increase in the aromatic fraction. These results may be related to the different properties of the feedstocks. Hydrogenation of the mono- and polycyclic aromatic compounds and the removal of some kinds of aromatic heteroatomic compounds may result in the decrease of the aromatic
(14) Liang, W. J. Petroleum Chemistry; Sinopec Press: Beijing, China, 1995. (15) Zhu, Z. H.; Qin, K. Z.; Wang, T. F.; Zhu, Y. J.; Zhang, Y. P. Preliminary study on hydrotreating of a high sulfur content shale oil. Proceedings of the International Conference on Oil Shale and Shale Oil; Chemical Industry Press: Beijing, China, 1988; p 451-460.
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Table 3. Elemental Analysis of the Distillates of the Fushun Shale Oil distillation range (°C)
distillate rate (wt %)
carbon (wt %)
hydrogen (wt %)
oxygen (wt %)
nitrogen (wt %)
sulfur (wt %)
-200 200-360 360-450 >450
2.95 41.55 36.25 19.25
82.28 84.75 84.65 84.14
12.14 12.05 12.04 10.91
4.19 1.64 1.36 2.38
0.67 1.01 1.30 1.67
0.72 0.55 0.65 0.90
Table 4. Results of the Diesel Distillate from Fushun Shale Oil and Hydrotreated Products Obtained over the CoMo Catalyst properties
density at 20 °C (g/mL) sulfur content (μg g-1) nitrogen content (μg g-1) bromine value (g of Br) cetane number saturated fraction (wt %) aromatic fraction (wt %) polar fraction (wt %) sulfur removal (%) nitrogen removal (%)
feedstock
0.8697 5516 9110 54.5 40.2 57.9 13.1 29.0
hydrotreated products at different conditions 320 °C
340 °C
360 °C
360 °C
4 MPa
4 MPa
4 MPa
5 MPa
1 h-1
1 h-1
1 h-1
1 h-1
600:1
600:1
600:1
600:1
0.8467 640 6559 25.5 50.9 67.5 12.8 19.7 88.4 28.0
0.8401 303 5539 20.8 53.9 72.8 11.8 15.4 94.5 39.2
0.8354 204 4837 15.4 56.1 76.2 10.9 12.9 96.3 46.9
0.8316 171 4528 14.0 57.9 78.9 10.5 10.6 96.9 50.3
Table 5. Results of the Diesel Distillate from Fushun Shale Oil and Hydrotreated Products Obtained over the NiW Catalyst properties
density at 20 °C (g/mL) sulfur content (μg g-1) nitrogen content (μg g-1) bromine value (g of Br) cetane number saturated fraction (wt %) aromatic fraction (wt %) polar fraction (wt %) sulfur removal (%) nitrogen removal (%)
feedstock
0.8697 5516 9110 54.5 40.2 57.9 13.1 29.0
hydrotreated products obtained at different conditions 320 °C
340 °C
360 °C
360 °C
4 MPa
4 MPa
4 MPa
5 MPa
1 h-1
1 h-1
1 h-1
1 h-1
600:1
600:1
600:1
600:1
0.8435 779 5842 25.3 52.3 70.3 12.2 17.5 85.9 35.9
0.8386 367 4581 19.7 54.6 75.2 11.3 13.5 93.3 49.7
0.8329 217 3118 12.2 57.3 78.6 10.1 11.3 96.1 65.8
0.8298 178 2391 10.3 58.7 81.0 9.8 9.2 96.8 73.8
Table 6. Results of the Diesel Distillate from Fushun Shale Oil and Hydrotreated Products Obtained over the NiMoW Catalyst properties
density at 20 °C (g/mL) sulfur content (μg g-1) nitrogen content (μg g-1) bromine value (g of Br) cetane number saturated fraction (wt %) aromatic fraction (wt %) polar fraction (wt %) sulfur removal (%) nitrogen removal (%)
feedstock
0.8697 5516 9110 54.5 40.2 57.9 13.1 29.0
hydrotreated products obtained at different conditions 320 °C
340 °C
360 °C
360 °C
4 MPa
4 MPa
4 MPa
5 MPa
1 h-1
1 h-1
1 h-1
1 h-1
600:1
600:1
600:1
600:1
0.8436 243 5654 24.8 52.3 68.9 12.6 18.6 95.6 37.9
0.8373 103 4218 18.8 55.2 78.7 9.5 11.8 98.1 53.7
0.8285 46 2308 12.4 59.3 81.2 9.0 9.8 99.2 74.7
0.8255 43 2038 10.1 60.7 84.6 8.2 8.2 99.2 77.6
follows: desulfurization activity of NiW < CoMo < NiMoW and denitrogenation activity of CoMo < NiW < NiMoW. The order of denitrogenation activity was also identical to hydrogenating activity, which determines the lowering of the density and bromine value and the increase of the cetane number.
However, nitrogen contents in products remained high. The products were not sufficiently stable even using the NiMoW catalyst. Additional experiments under more severe conditions should be carried out to obtain high-quality products. The results were shown in Table 7. 4422
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Table 7. Results of the Diesel Distillate from Fushun Shale Oil and Hydrotreated Products Obtained over the NiMoW Catalyst at More Severe Conditions properties
density at 20 °C (g/mL) sulfur content (μg g-1) nitrogen content (μg g-1) bromine value (g of Br) cetane number saturated fraction (wt %) aromatic fraction (wt %) polar fraction (wt %) sulfur removal (%) nitrogen removal (%)
feedstock
0.8697 5516 9110 54.5 40.2 57.9 13.1 29.0
hydrotreated products obtained at different conditions 360 °C
340 °C
360 °C
6 MPa 1 h-1
7 MPa 0.5 h-1
6 MPa 0.5 h-1
1000:1
1000:1
1000:1
0.8162 42 853 2.5 65.0 86.6 7.4 6.0 99.2 90.6
0.8158 40 750 2.3 65.2 87.9 6.8 5.3 99.3 91.8
0.8155 41 195 1.6 65.3 90.3 6.7 3.0 99.3 97.9
Figure 2. Gas chromatogram of the Fushun shale oil distillate.
Figure 3. Gas chromatogram of the hydrotreated diesel distillte at the most severe conditions.
In Table 7, the sulfur contents in hydrotreated products were not significantly decreased at more severe conditions. This implied that the unreacted sulfur species were quite refractory. The extent of denitrogenation became higher. In the hydrotreated product, the nitrogen content of 195 μg g-1 at the most severe conditions (360 °C, 6 MPa, 0.5 h-1, and 1000:1) can be obtained, which corresponded to denitrogenation of 98.1%. A lighter oil was therefore produced from catalytic hydrotreating of the shale oil distillate, with a lower content of alkene and aromatic fraction and with a higher cetane number. All of the three products were stable in color and did not darken for months.
Figures 2 and 3 show the gas chromatogram of the diesel distillate and hydrotreated oil using the NiMoW catalyst at the most severe conditions (360 °C, 6 MPa, 0.5 h-1, and 1000:1), respectively. Figure 2 showed the characteristic peaks of aliphatic hydrocarbons. They consisted of double peaks concerning alkanes and alkenes together with other aliphatic compounds, such as, branched compounds. The hydrocarbons detected by the system ranged from C11 to C23. However, after catalytic hydrotreating, some lower molecular-weight compounds were produced. In addition, the peaks of alkane increased significantly in Figure 3 compared to the raw distillate in 4423
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Figure 2. Significantly, the peaks of alkene, dominant in the raw diesel distillate, were markedly reduced.
converted during the catalytic hydroprocessing. However, denitrogenation was much more difficult than desulfurization, even at severe conditions. The comparison of the three types of catalysts revealed that the NiMoW catalyst was most active for heteroatom removal in the three catalysts. Under relative mild conditions, it was possible to produce very stable oil from the Fushun shale oil distillate. After hydrogenation, produced oil had low contents of sulfur (41 μg g-1), nitrogen (195 μg g-1), and alkene, reduced density, and increased cetane number. The hydrotreated product can be directly used as a domestic transportation fuel.
4. Conclusions Catalytic hydrotreating of the diesel distillate from Fushun shale oil was investigated using three types of catalysts at different conditions. The results showed that the degrees of sulfur removal were high for all of the three catalysts, even at moderate conditions. It indicated that most of the sulfur species in this distillate were reactive, which can be easily
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