Energy Fuels 2010, 24, 4111–4115 Published on Web 06/08/2010
: DOI:10.1021/ef100392d
Highly Effective F-Modified HZSM-5 Catalysts for the Cracking of Naphtha To Produce Light Olefins Xiang Feng, Guiyuan Jiang,* Zhen Zhao,* Lei Wang, Xianghu Li, Aijun Duan, Jian Liu, Chunming Xu, and Jinsen Gao State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing 102249, China Received March 30, 2010. Revised Manuscript Received May 13, 2010
A series of fluorinated HZSM-5 zeolites (F/HZSM-5) were prepared by immersing the zeolites with different concentrations of NH4F solution, and their performances for the catalytic cracking of naphtha to produce light olefins were investigated. The results indicated that F-modified HZSM-5 zeolites are effective catalysts for the cracking of naphtha to light olefins. At the temperature of 600 °C, the yields of propene and ethene were achieved at 36.4 and 20.2%, which were 7.3 and 4.3% higher than those over parent HZSM-5 zeolite, respectively. The physicochemical features of F/HZSM-5 catalysts were characterized by means of X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), temperature-programmed desorption of ammonia (NH3-TPD), Fourier transform infrared (FTIR) spectra of adsorbed pyridine, etc. The results indicated that fluorine (F) modification not only regulates the pore characteristics of the HZSM-5 zeolites but also modulates the amount of acid sites, especially the amount of Br€ onsted (B) acid. Consequently, F modification with suitable content was favorable for increasing the conversion of naphtha and enhancing the selectivity to light olefins.
cracking (FCC) processes,9-13 etc. Among them, the catalytic cracking technique, because of its prominent ability to reduce the reaction temperature and adjust the product distribution, has been considered as an attractive alternative to produce ethene and propene.14,15 Thus far, various feedstocks have been used for catalytic cracking to produce light olefins, including naphtha,2,3 heavy oil,16-18 C4 hydrocarbons,19-24 etc. Among them, the conventional naphtha is most attractive, not only because it can take advantage of the existing facilities that are used for steam cracking but also because naphtha behaves as an intermediate
1. Introduction Light olefins, such as ethene and propene, are important building blocks of the petrochemical industry, and they are mostly used as starting materials for the production of various chemicals and polymers.1 In recent years, driven by the increasing use and wide application of polyolefins, the demand for light olefins (particularly propene) is growing rapidly. Presently, ethene and propene are mainly produced by naphtha steam cracking.2 However, because of the thermal cracking character, steam cracking always requires high reaction temperatures (over 800 °C), which makes it become the first energy-consuming process in the petrochemical industry by consuming nearly 40% of the total energy used by this field.3 Furthermore, steam cracking also has a strict limit for feedstock and low selectivity to alkenes. To enhance the yields of ethene and propene with less energy consumption, many processes have been proposed, including dehydrogenation of ethane and propane,4 the metathesis of ethene and butene,5 methanol to olefin (MTO),6-8 some special fluidized catalytic
(9) Xie, C. G. Pet. Technol. 1997, 26, 825. (10) Han, W. D.; Huang, R. K.; Gong, J. H. Pet. Refin. Eng. 2006, 36, 1. (11) Henry, B. E.; Wachter, W. A.; Swan, G. A. U.S. Patent 7,261,807, 2007. (12) Li, C. Y.; Yang, C. H.; Shan, H. H. Ind. Eng. Chem. Res. 2007, 46, 4914–4920. (13) Corma, A.; Melo, F. V.; Sauvanaud, L.; Ortega, F. Catal. Today 2005, 107-108, 699–706. (14) Jiang, G. Y.; Zhang, L.; Zhao, Z.; Zhou, X. Y.; Duan, A. J.; Xu, C. M.; Gao, J. S. Appl. Catal., A 2008, 340, 176–182. (15) Meng, X. H.; Gao, J. S.; Li, L.; Xu, C. M. Pet. Sci. Technol. 2004, 22, 1327–1341. (16) Meng, X. H.; Xu, C. M.; Gao, J. S.; Li, L. Catal. Commun. 2007, 8, 1197–1201. (17) Sha, Y. S.; Cui, Z. Q.; Wang, M. D.; Wang, L. Y.; Wang, G. L.; Zhang, J. Pet. Process. Petrochem. 2000, 31, 29–32. (18) Shi, Z. C.; Zhang, F. M.; Liu, S. H. U.S. Patent 6,211,104, 2001. (19) Zhu, X. X.; Li, X. J.; Xie, S. J.; Liu, S. L.; Xu, G. L.; Xin, W. J.; Huang, S. J.; Xu, L. Y. Catal. Surv. Asia 2009, 13, 1–8. (20) Wang, B.; Gao, Q.; Gao, J. D.; Ji, D.; Wang, X. L.; Suo, J. H. Appl. Catal., A 2004, 274, 167–172. (21) Tang, X. P.; Zhou, H. Q.; Qian, W. Z.; Wang, D. Z.; Jin, Y.; Wei, F. Catal. Lett. 2008, 125, 380–385. (22) Wakui, K.; Satoh, K.; Sawada, G.; Shiozawa, K.; Matano, K.; Suzuki, K.; Hayakawa, T.; Yoshimura, Y.; Murata, K.; Mizukami, F. Appl. Catal., A 2002, 230, 195–202. (23) Zhao, G. L.; Teng, J. W.; Xie, Z. K.; Jin, W. Q.; Yang, W. M.; Chen, Q. L.; Tang, Y. J. Catal. 2007, 248, 29–37. (24) Lu, J. Y.; Zhao, Z.; Xu., C. M.; Zhang., P.; Duan, A. J. Catal. Commun. 2006, 7, 199–203.
*To whom correspondence should be addressed. Telephone: þ86-1089731586. Fax: þ86-10-69724721. E-mail:
[email protected] (G.J.);
[email protected] (Z.Z.). (1) Plotkin, J. S. Catal. Today 2005, 106, 10–14. (2) Wan, J. L.; Wei, Y. X.; Liu, Z. M.; Li, B.; Qi, Y.; Li, M. Z.; Xie, P.; Meng, S. H.; He, Y. L.; Chang, F. X. Catal. Lett. 2008, 124, 150–156. (3) Yoshimura, Y.; Kijima, N.; Hayakawa, T.; Murata, K.; Suzuki, K.; Mizukami, F.; Matano, K.; Konishi, T.; Oikawa, T.; Saito, M.; Shiojima, T.; Shiozawa, K.; Wakui, K.; Sawada, G.; Sato, K.; Matsuo, S.; Yamaoka, N. Catal. Surv. Jpn. 2000, 4, 157–167. (4) Heineke, D.; Baier, M.; Demuth, D.; Harth, K. U.S. Patent 6,989,346 B2, 2006. (5) Schwab, P.; Schulz, R.; Schulz, M.; Breitscheidel, B.; Meyer, G. U. S. Patent 6,166,279, 2000. (6) St€ ocker, M. Microporous Mesoporous Mater. 1999, 29, 3–48. (7) Cui, Z. M.; Liu, Q.; Song, W. G.; Wan, L. J. Angew. Chem., Int. Ed. 2006, 45, 6512–6515. (8) Liu, G. Y.; Tian, P.; Li, J. Z.; Zhang, D. Z.; Zhou, F.; Liu, Z. M. Microporous Mesoporous Mater. 2008, 111, 143–149. r 2010 American Chemical Society
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product of the heavy oil catalytic cracking, and the study of it can provide further understanding and new enlightenment on this process. From another view, the catalyst plays an important role in enhancing the yield of light olefins, and a series of effective catalysts, including ZSM-5,2,14,22-24 BEA,25 MCM22,26 etc., has been studied. Jung et al.27 investigated the catalytic cracking of n-octane over zeolites with different pore structures and acidities and found that MFI zeolite with sinusoidal pores and more strong acid sites exhibited continuous and high catalytic activity. Recent studies on HZSM-5 for catalytic cracking mainly focused on the post-treatment28,29 and element modification.14,22-24 Among the many compounds for element modification, the incorporation of F species as electronwithdrawing compounds to HZSM-5 zeolites to enhance the surface acidity shows promise.30 Mao et al.31 investigated ZSM5 zeolites doped with fluorine species and activated at different temperatures and found that F modification with low content and suitable activation temperature could bring about new Br€ onsted (B) acid sites and strengthen some acid sites of the parent zeolite without damaging the crystalline structure. Wang and co-authors32 studied the influence of the calcination temperature on the stability of fluorinated nano-sized HZSM-5. It was found that controlling the calcination temperature can modulate the ratio of Br€ onsted/Lewis (B/L) acids and the acid strength of the catalyst, and the fluorinated nanosized HZSM-5 exhibited better stability in the methylation of biphenyl with methanol. Despite these remarkable achievements, the application of F-modified HZSM-5 in other suitable reactions and further elucidating their promoting mechanism are still indispensable. Therefore, in this study, to increase the yields of ethene and propene by catalytic cracking of naphtha and also to find whether F-modified HZSM-5 are effective for this reaction, a series of F-modified HZSM-5 samples (F/HZSM-5) was prepared and their catalytic performances for the cracking of naphtha were investigated. The correlation between the physicochemical properties of the studied catalysts and their catalytic performances was also discussed.
marked as 1-4 according to the different concentrations of NH4F solution correspondingly, and the HZSM-5 parent sample calcined at 700 °C in an air atmosphere for 5 h was marked as 0. The samples were pressed and crushed to particles of 40-60 mesh for catalytic testing and characterization. 2.2. Catalytic Activity Measurement. The catalytic reaction was carried out in a fixed-bed flow reactor by pumping naphtha (detailed properties of this feedstock are listed in Table S1 in the Supporting Information) at a flow rate of 0.3 mL h-1, diluted by N2 flow at a flow rate 400 mL min-1 over 750 mg of catalyst (total pressure of 1 atm). The products were analyzed online using a gas chromatograph (SP-2100) equipped with a 50 m PONA capillary column and a flame ionization detector (FID). The data were collected after 10 min on stream, and the selectivity is calculated on a carbon basis. 2.3. Catalyst Characterization. The crystallinity of the samples was determined on a SHIMADZU-6000 diffractometer, using Cu KR radiation at 40 kV and 30 mA, with a scanning rate of 2°/min. The Brunauer-Emmett-Teller (BET) specific surface area and pore volume of the catalysts were measured with linear parts of the BET plot of N2 adsorption isotherms, using a Micromeritics ASAP 2010 instrument. Acidic amounts of the zeolite were measured by the temperature-programmed desorption of ammonia (NH3-TPD) method. A total of 0.2 g of sample with 40-60 mesh was pretreated in helium at 500 °C for 2 h, cooled to 120 °C, and adsorbed NH3 for 30 min. After flushing by pure helium gas at 120 °C for 1 h, TPD started at a rate of 5 °C/min from 120 to 700 °C and the signal was monitored with a thermal conductivity detector (TCD). Fourier transform infrared (FTIR) spectra of pyridine adsorption were conducted by the FTIR spectrometer (Nicolet AVATAR 360 FTIR), equipped with an in situ cell containing CaF2 windows. The Br€ onsted and Lewis acid sites could be distinguished by the bands of chemisorbed pyridinium ion at different wavenumbers.
3. Results and Discussion 3.1. Catalytic Performances of F/HZSM-5 for the Cracking of Naphtha. Table 1 presents the activity and selectivity of F/HZSM-5 zeolites treated with different concentrations of NH4F solution for the cracking of naphtha to light olefins. From Table 1, it can be seen that, with increasing reaction temperatures, the conversion of the naphatha increased. In comparison to that on parent HZSM-5, the conversion of naphtha was improved on F/HZSM-5 at most temperatures, indicating that F modification enhanced the activity of the catalysts. In addition, the highest conversion was obtained over sample 2. In the studied temperature range, with increasing reaction temperatures, the selectivity to methane and ethene increased and the selectivity to propene and butene decreased. In addition, the selectivity to ethane and propane was relatively low. The selectivity data on HZSM-5 zeolites before and after F modification show that, in the same temperature range, after F modification, the selectivity to methane, butene, and arene decreased, while the selectivity to ethene and propene increased obviously. At the temperature of 550 °C, the maximum selectivity to ethene plus propene of 56.4% was obtained, which was 8.5% higher than that on parent HZSM-5. Figure 1a shows the yields of ethene in the catalytic cracking of naphtha over parent and F-modified HZSM-5 catalysts. From Figure 1a, it can be seen that the yields of ethene over F/HZSM-5 were higher than that on the unmodified HZSM-5 catalyst, especially at the temperatures lower than 600 °C. At 600 °C, the maximum yield of ethene of 20.2% was achieved on catalyst 2, which was 4.3% higher than that
2. Experimental Section 2.1. Catalyst Preparation. HZSM-5 zeolite was purchased from Shanghai Aoqian Company (Si/Al ratio of 46). F-Modified HZSM-5 samples were prepared by immersing the HZSM5 zeolite in an aqueous solution of NH4F. The concentrations of the NH4F solution were 0.01, 0.1, 0.3, and 1.0 M, and the immerse period lasted for 4 h with continuous stirring at 35 °C. Then, the samples were filtrated, washed by pure water, finally dried at 120 °C, and calcined at 700 °C in an air atmosphere for 5 h. After finishing the preparation of the catalysts, they were (25) Nakao, R.; Kubota, Y.; Katada, N.; Nishiyama, N.; Kunimori, K.; Tomishige, K. Catal. Lett. 2003, 89, 153–157. (26) Zhu, X. X.; Liu, S. L.; Song, Y. Q.; Xie, S. J.; Xu, L. Y. Appl. Catal., A 2005, 290, 191–199. (27) Jung, J. S.; Kim, T. J.; Seo, G. Korean J. Chem. Eng. 2004, 21, 777–781. (28) Lu, J. Y.; Zhao, Z.; Xu, C. M.; Duan, A. J.; Zhang, P. J. Nat. Gas Chem. 2005, 14, 213–220. (29) Jung, J. S.; Park, J. W.; Seo, G. Appl. Catal., A 2005, 288, 149–157. (30) Kogelbauer, A.; Nikolopoulos, A. A.; Goodwin, J. G.; Marcelin, G., Jr. In Zeolites and Related Microporous Matericals: State of the Art; Weitkamp, J., Karge, H. G., Pfeifer, H., Holderich, W., Eds.; Elsevier Science Ltd.: Amsterdam, The Netherlands, 1994; pp 1-1685. (31) Le Van Mao, R.; Le, T. S.; Fairbairn, M.; Muntasar, A.; Xiao, S.; Denes, G. Appl. Catal., A 1999, 185, 41–52. (32) Wang, Y. N.; Guo, X. W.; Zhang, C.; Song, F. L.; Wang, X. S.; Liu, H. O.; Xu, X. C.; Song, C. S.; Zhang, W. P.; Liu, X. M.; Han, X. W.; Bao, X. H. Catal. Lett. 2006, 107, 209–214.
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Table 1. Activity and Selectivity of F/HZSM-5 Catalysts for the Cracking of Naphtha to Light Olefins selectivity (%) samples
0
1
2
3
4 a
temperature (°C)
conversion (%)
CH4
C2H4
C2H6
C3H6
C3H8
C4H8a
areneb
550 600 650 700 550 600 650 700 550 600 650 700 550 600 650 700 550 600 650 700
73.3 85.7 94.2 93.7 75.5 92.3 93.2 95.1 75.8 93.4 96.6 96.0 74.0 85.0 94.2 96.2 76.5 91.8 92.9 94.5
2.6 4.0 4.7 5.9 1.8 3.3 4.3 5.2 1.8 3.1 4.5 5.2 2.2 3.5 5.2 5.5 2.4 3.7 4.8 8.1
12.3 18.5 25.6 31.8 14.5 18.5 24.6 31.2 17.4 21.6 27.9 33.7 15.9 18.8 25.2 31.9 15.8 20.0 24.1 32.5
0.9 0.9 0.9 1.2 1.6 1.4 1.4 1.3 1.9 1.7 1.9 1.7 1.6 1.4 1.5 1.3 1.6 1.4 1.5 1.8
35.6 33.9 32.2 25.7 36.8 37.8 35.8 31.1 39.0 39.0 35.0 31.2 39.0 37.0 34.0 30.8 39.2 37.5 35.7 27.7
1.6 1.4 1.2 0.7 2.4 1.9 1.6 1.0 2.9 2.1 1.8 0.9 2.5 1.9 1.7 0.9 2.5 1.9 1.8 1.0
16.8 10.4 5.1 1.8 11.7 9.5 5.1 1.8 10.6 7.8 3.6 1.6 12.2 8.8 4.4 1.7 11.7 8.1 7.1 0.8
27.8 29.8 29.9 32.6 28.4 25.8 26.6 28.3 23.5 23.3 24.7 25.7 23.9 27.1 27.6 27.7 24.2 26.2 24.1 28.1
Butene (C4H8) was mainly 1-butene and 2-butene (including trans,2-butene and cis,2-butene). b Arene included benzene, toluene, and xylene.
Figure 2. XRD patterns of the samples.
reached 36.4% over catalyst 2 at 600 °C, which was 7.3% higher than that on the unmodified HZSM-5 catalyst. The yield of ethene plus propene as a function of the reaction time over parent HZSM-5 and F/HZSM-5 (see Figure S1 in the Supporting Information) shows that F modification does not change the stability of the HZSM-5 zeolite. 3.2. Structural Properties. Figure 2 shows the X-ray diffraction (XRD) patterns of HZSM-5 samples before and after F modification. From Figure 2, it can be seen that the X-ray powder patterns of the samples are typical of the MFI topology. In comparison to the parent HZSM-5 catalyst, there are no peaks of impurities and other obvious crystalline changes for F/HZSM-5 samples, indicating that F/HZSM-5 samples keep well the framework structure of HZSM-5. The specific surface area and pore volume of F/HZSM-5 catalyst samples were investigated according to the BET method from the nitrogen adsorption isotherms, and the corresponding data are summarized in Table 2. From Table 2, it can be seen that the BET surface area and pore volume of F/HZSM-5 increased in comparison to parent HZSM-5. Further detailed data on micropore surface area and pore volume show that the increase in the total BET surface area and pore volume is mainly from the increase in those on the micropore. Such an enhanced effect shows that the NH4F treatment could create some secondary
Figure 1. Yield of (a) ethene and (b) propene over F/HZSM-5 as a function of the temperature for the catalytic cracking of naphtha.
on HZSM-5. Different from the trends on ethene, the yield of propene shown in Figure 1b increased first and then decreased with further increasing of the reaction temperature. This is due to the fact that, for the catalytic cracking reaction, propene is the intermediate product. Further increasing the reaction temperature will facilitate the secondary reactions and consequently lower its yield. From Figure 1b, it can also be seen that the yields of propene over F/HZSM-5 were obviously higher than that on the unmodified HZSM-5 catalyst at each temperature. The maximum propene yield 4113
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Table 2. Effect of F Modification on the Surface Area and Pore Volume of HZSM-5
Table 3. Amount of B and L Acid Sites Determined by Pyridine Adsorption for F/HZSM-5 and HZSM-5 Samples at Different Degassed Temperatures
t-method total pore t-method BET surface micropore surface volume micropore 2 -1 2 -1 -1 samples area (m g ) area (m g ) (mL g ) volume (mL g-1) 0 1 2 3 4
312.2 336.0 356.4 349.4 342.8
281.0 308.2 327.6 306.2 316.1
0.183 0.192 0.204 0.211 0.195
amount of acid sites (200 °C) (a.u./g cm-2)
0.139 0.153 0.160 0.150 0.155
amount of acid sites (350 °C) (a.u./g cm-2)
samples
B
L
BþL
B
L
BþL
0 1 2 3 4
68.4 129.2 177.8 152.1 147.7
30.0 97.9 70.6 94.5 70.1
98.4 227.1 248.4 246.6 217.8
28.7 46.8 67.0 53.9 63.3
11.8 53.5 39.5 53.2 36.5
40.5 100.3 106.5 107.1 99.8
increased the acid amount of HZSM-5, regardless of the total or medium and strong acids. For acid type in detail, both the amounts of B and L acids were enhanced. The increase in the B acid amount could be ascribed to the formation of new acidic hydroxyl groups by the reaction of the zeolite surface with the protons of the remaining (Hþ 3 3 3 F-) ion pairs and the regulation from F on the local environment (electronwithdrawing effect of F) of bridged hydroxyl groups.31 The promotion mechanism on L acid is tentatively assumed to be related to the effect of F on Al species. Among the F-modified HZSM-5 samples, catalyst 2 possesses the largest B acid amount. In combination of this with the fact that the maximal yield of propene was achieved on catalyst 2, shown in Figure 1b, it can be concluded that a larger amount of acid sites, especially B acid sites, is favorable for obtaining a high yield of light olefins. Considering the increase in the BET surface area and pore volume by F treatment, as mentioned in Table 2, all of these indicate that the incorporation of F species to HZSM-5 zeolites not only dredges the channels but also modulates the total amount of acid sites, especially the amount of B acid sites, which in turn promotes the catalytic performances of HZSM-5 for the catalytic cracking of naphtha.
Figure 3. NH3-TPD profiles of F/HZSM-5 catalysts.
pore or dredge the channels of the HZSM-5 zeolites, which may result from the induced dissolution of amorphous substances in HZSM-5 pores by HF species generated from the decomposition of NH4F.33 3.3. NH3-TPD Profiles of F/HZSM-5 Catalysts. Figure 3 presents the NH3-TPD profiles of the parent and F-modified HZSM-5 catalysts. From Figure 3, it can be seen that there are two desorption group peaks for HZSM-5, one centered at 150-250 °C and the other at 350-500 °C, corresponding to the weak and strong acid sites, respectively. Upon modification by F, the amount of weak and strong acids of F/HZSM-5 showed an obvious increase, which accompanied the emergence of desorption peaks for strong acid sites, indicating that F modification can improve the acid amount of HZSM-5 and might also introduce some new strong acid sites.31 As a result, the increase in the amount of acid sites after F modification brings about the increase in the conversion of naphtha and also increases the selectivity to propene. 3.4. FTIR of Pyridine Adsorption on F/HZSM-5 Catalysts. The Br€ onsted and Lewis acidities of the samples were determined by FTIR spectroscopy of pyridine adsorption. All samples exhibited characteristic bands at about 1540 and 1450 cm-1, which are assigned to pyridine adsorbed on the B and L acid sites, respectively.34,35 Table 3 shows the adsorption amounts of pyridine, which were degassed at 200 and 350 °C. The adsorption amount of pyridine on the sample degassed at the temperature of 200 °C corresponds to the total acid amount, while the adsorption amount of pyridine on the sample degassed at relatively high temperature of 350 °C corresponds to the acid amount of strong- and medium-strength acid. From Table 3, it can be seen that, in comparison to parent HZSM-5, F modification remarkably
4. Conclusions A series of HZSM-5 zeolites treated by different concentrations of NH4F solution was prepared, and their performances for the catalytic cracking of naphtha to produce light olefins were investigated. The results showed that the introduction of F into HZSM-5 zeolite enhanced the selectivity to light olefins and, thus, increased the yield of light olefins in the catalytic cracking of naphtha. At the temperature of 600 °C, the yields of propene and ethene were achieved at 36.4 and 20.2%, which were higher than those over parent HZSM-5 by 7.3 and 4.3%, respectively. XRD and BET characterization on F/HZSM-5 catalysts showed that the framework structure of HZSM-5 was scarcely damaged after F modification and that F modification can increase the surface area and pore volume of HZSM-5 zeolites. Acidity characterization on F/HZSM-5 samples indicated that the incorporation of F species could modulate the amount of acid sites, especially the amount of B acid sites, which is favorable for obtaining a high conversion of naphtha and high selectivity to as well as high yield of light olefins. The fact that fluorine addition could regulate both the pore and acidic characteristics of HZSM-5 zeolites, which in turn promoted its catalytic performance, will throw new light on the design of novel catalysts with multifunctional post-treatment or post-modification for the production of light olefins.
(33) Zhao, G. L.; Teng, J. W.; Xie, Z. K.; Tang, Y.; Yang, W. M.; Chen, Q. L. Chin. J. Catal. 2005, 26, 1083–1087. (34) Poncelet, G.; Dubru, M. L. J. Catal. 1978, 52, 321–331. (35) Lee, J. S.; Boudart, M. Catal. Lett. 1993, 20, 97–106.
Acknowledgment. This work was supported by the National Natural Science Foundation of China (20806092), the Key 4114
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Supporting Information Available: Main properties of the feedstock (Table S1) and the yield of ethene plus propene as a function of the reaction time over HZSM-5 and F/HZSM-5 (sample 2) at 600 °C (Figure S1). This material is available free of charge via the Internet at http://pubs.acs.org.
Project of Chinese Ministry of Education (307008), the PetroChina Innovation Fund (07-06D-01-04-04-04), the Specialized Research Fund for the Doctoral Program of Higher Education (20070425010), and the State Key Laboratory of Heavy Oil Processing, China University of Petroleum.
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