Catalytic and Thermal Pyrolysis of Atmospheric Residue - Energy

Energy & Fuels 2009, 23, 65–69

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Catalytic and Thermal Pyrolysis of Atmospheric Residue Xianghai Meng, Chunming Xu, Jinsen Gao,* Li Li, and Zhichang Liu State Key Laboratory of HeaVy Oil Processing, China UniVersity of Petroleum, Beijing 102249, China ReceiVed August 21, 2008. ReVised Manuscript ReceiVed NoVember 3, 2008

Pyrolysis of Chinese Daqing atmospheric residue on the commercial catalytic pyrolysis process (CPP) catalyst, commercial fluid catalytic cracking (FCC) catalyst, and quartz sand was investigated using a confined fluidized bed reactor system. The pyrolysis behaviors of the commercial CPP catalyst were similar to those of the commercial FCC catalyst, while they were different from those of quartz sand. The reaction extent of the thermal pyrolysis on quartz sand was high, and the yield of total light olefins was 36.88 wt % at 660 °C and 41.88 wt % at 700 °C. The commercial CPP catalyst showed the best pyrolysis performance and obtained the highest yield of total light olefins. The use of catalysts accelerates not only the cracking reaction, but also the hydrogen transfer and isomerization reactions. Both the free radical mechanism and the carbonium ion mechanism play an important role for the catalytic pyrolysis of Daqing atmospheric residue for light olefin production.

1. Introduction Catalytic pyrolysis can be used to produce light olefins such as ethylene, propylene, and butylene from a wide range of low value feedstocks, such as heavy oils.1-3 With the increased demand for light olefins and the lack of feedstock from the conventional source, catalytic pyrolysis has attracted great interest in recent years.4,5 Compared with the conventional thermal pyrolysis, catalytic pyrolysis has the potential of reducing energy cost by operating at lower temperature and using a variety of feedstocks. Heavy oil is a relatively low value refinery feedstock. The challenge is to add value to this opportunity feedstock. The process of the catalytic pyrolysis of heavy oil is complicated, and many factors have an influence on the product yield and distribution.1-3,6-8 One of the most important aspects of understanding the catalytic pyrolysis of heavy oil is its mechanistic pathway, but unfortunately, there has not been a uniform viewpoint for the catalytic pyrolysis mechanism of heavy oil so far. Some researchers consider that the catalytic * To whom correspondence should be addressed. Telephone: 8610-89733993. Fax: 8610-6972-4721. E-mail: [email protected]. (1) Sha, Y. X.; Cui, Z. Q.; Wang, M. D.; Wang, G. L.; Zhang, J. Olefin production by heavy-oil contact cracking. Petrochem. Technol. 1999, 28 (9), 618–621. (2) Zhang, Z. G.; Xie, C. G.; Shi, Z. C.; Wang, Y. M. Study on catalytic pyrolysis process for ethylene and propylene production. Pet. Process. Petrochem. 2001, 32 (5), 21–24. (3) Meng, X. H.; Xu, C. M.; Gao, J. S.; Li, L. Studies on catalytic pyrolysis of heavy oils: Reaction behaviors and mechanistic pathways. Appl. Catal., A 2005, 294, 168–176. (4) Li, X. M.; Song, F. R. Advances in olefin production technology by catalytic cracking. Petrochem. Technol. 2002, 31 (7), 569–573. (5) Meng, X. H.; Gao, J. S.; Li, L.; Xu, C. M. Advances in catalytic pyrolysis of hydrocarbons. Pet. Sci. Technol. 2004, 22 (9, 10), 1327–1341. (6) Basily, I. K.; El-Shaltawy, S. T.; Mostafa, B. S. The catalytic pyrolysis of the Egyptian bitumen for industrial production raw material. J. Anal. Appl. Pyrolysis 2006, 76, 24–31. (7) Li, X. F.; Shen, B. J.; Guo, Q. X.; Gao, J. S. Effects of large pore zeolite additions in the catalytic pyrolysis catalyst on the light olefins production. Catal. Today 2007, 125, 270–277. (8) Meng, X. H.; Xu, C. M.; Gao, J. S.; Zhang, Q. Effect of catalyst to oil weight ratio on gaseous product distribution during heavy oil catalytic pyrolysis. Chem. Eng. Process. 2004, 43, 965–970.

pyrolysis of hydrocarbons follows the free radical mechanism,9,10 others consider that the catalytic pyrolysis on acidic molecular sieve catalysts proceeds by the carbonium ion mechanism,11,12 and still another group of researchers believes that the catalytic pyrolysis on acidic molecular sieve catalysts follows both the carbonium ion and free radical mechanisms.13,14 The reaction temperature of catalytic pyrolysis is usually high. Therefore, it is necessary to investigate and compare the reaction performance of catalytic pyrolysis and thermal pyrolysis to study the reaction mechanism of the catalytic pyrolysis of hydrocarbons. In this paper we investigate the reaction performance of the catalytic pyrolysis and thermal pyrolysis of atmospheric residue and then compare the yields of light olefins, the hydrogen transfer and isomerization coefficients, and the mechanism parameter to reveal the reaction mechanism of the catalytic pyrolysis of heavy oil. 2. Experimental Section 2.1. Feedstocks and Catalyst. Chinese Daqing atmospheric residue (Daqing AR) was used as the feedstock. The key properties of Daqing AR are given in Table 1. A commercial catalytic pyrolysis process (CPP) catalyst developed by the SINOPEC Research Institute of Petroleum Processing and a commercial fluid catalytic cracking (FCC) catalyst were used in the tests. The properties of the commercial CPP and FCC catalysts are listed in (9) Erofeev, V. I.; Adyaeva, L. V.; Ryabov, Y. V. Pyrolysis of straightrun naphtha on ZSM-5 zeolites modified with alkaline-earth metal cations. Russ. J. Appl. Chem. 2001, 74 (2), 235–237. (10) Lemonidou, A. A.; Vasalos, I. A.; Hirschberg, E. J.; Bertolacini, R. J. Catalyst evaluation and kinetic study for ethylene production. Ind. Eng. Chem. Res. 1989, 28, 524–530. (11) Li, A. T. Deep catalytic cracking technology bridging petroleum processing with chemical industry. Chin. Eng. Sci. 1999, 1 (2), 67–71. (12) Wang, X. Q.; Jiang, F. K. Features and prospects of several gaseous olefin production processes with heavy oil as feedstock. Pet. Process. Petrochem. 1994, 25 (1), 1–8. (13) Xie, C. G. Studies on catalytic pyrolysis process for ethylene production and its reaction mechanism. Pet. Process. Petrochem. 2000, 31 (7), 40–44. (14) Xie, C. G.; Pan, R. N. Studies on producing ethylene and propylene from heavy hydrocarbons by catalytic pyrolysis process. Pet. Process. Petrochem. 1994, 25 (6), 30–34.

10.1021/ef8006867 CCC: $40.75  2009 American Chemical Society Published on Web 12/16/2008

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Table 1. Properties of Chinese Daqing Atmospheric Residue property

value

density(20 °C), g/cm3 carbon residue content, wt % mean relative molecular mass hydrogen content, wt % carbon content, wt % H/C atomic ratio aromaticity, % group analysis (content, wt %) saturates aromatics resins and asphaltenes

0.9069 4.3 577 13.11 86.52 1.82 10.90 57.1 27.6 15.3

Table 2. Properties of the Commercial CPP and FCC Catalysts catalyst microactivity index pore volume, cm3/g surface area, m2/g packing density, g/cm3 particle density, g/cm3 particle size distribution, wt % 0-20 µm 20-40 µm 40-80 µm >80 µm

commercial CPP catalyst

commercial FCC catalyst

70 0.19 80 0.97 1.5

57 0.092 77 0.91

1.2 13.4 55.9 29.5

1.4 10.6 49.0 39.0

Table 2. The surface area and pore volume of quartz sand (74-150 µm) are 4 m2/g and 0.003 cm3/g, respectively. 2.2. Apparatus and Experimental Conditions. Figure 1 shows the confined fluidized bed reactor system for the pyrolysis experiments. It is comprised of five sections: oil and steam input systems, a reaction zone, a temperature control system, and a product separation and collection system. Experiments are conducted in the batch mode. For each experiment, 50 g of catalyst was loaded into the reactor with an effective volume of about 580 mL. Distilled water was pumped into a furnace to generate steam, which was used to fluidize the catalyst in the reactor. The feedstock was pumped and mixed with the steam. The mixture was heated to approximately 500 °C in a preheater and then entered the reactor. Reactions took place as the feed contacted with the fluidized catalyst. The reaction product was cooled and separated into liquid and gas samples. The spent catalyst after reaction was drawn from the reactor by a vacuum pump. The pyrolysis experiments were carried out by varying the reaction temperature from 600 to 700 °C while keeping the residence time, catalyst-to-oil weight ratio, and steam-to-oil weight ratio constant at 3 s, 17, and 0.8, respectively. 2.3. Analytical Methods. An Agilent 6890 gas chromatograph with a hydrogen flame ionization detector, a thermal conductivity

Figure 1. Diagram of the experimental setup (1, constant-temperature box; 2, steam furnace; 3, feedstock; 4, electronic balance; 5, oil pump; 6, water tank; 7, water pump; 8, preheater; 9, reactor furnace; 10, thermocouple; 11, reactor; 12, inlet and outlet of catalysts; 13, filter; 14, condenser; 15, collecting bottle for liquid products; 16, gas collection vessel; 17, beaker; 18, gas sample bag).

Table 3. Product Yields of the Catalytic Pyrolysis of Daqing AR on the Commercial CPP Catalyst, wt %

dry gas LPG gasoline + diesel heavy oil coke conversion

600 °C reaction temp




17.79 40.46 27.89 3.83 10.02 96.17

23.04 39.52 22.91 3.63 10.90 96.37

27.53 38.26 18.84 3.39 11.98 96.61

37.25 30.28 16.52 2.49 13.46 97.51

Table 4. Yields of the Components in Pyrolysis Gas of the Catalytic Pyrolysis of Daqing AR on the Commercial CPP Catalyst, wt %

ethylene propylene butylene total light olefins carbon oxides hydrogen methane ethane propane butane





10.21 19.77 11.02 41.00 1.96 0.25 3.06 2.32 4.84 4.83

12.48 21.56 10.93 44.98 2.46 0.36 4.64 3.10 3.94 3.09

14.72 22.43 10.45 47.59 2.09 0.47 6.60 3.66 3.15 2.23

18.23 19.69 7.75 45.67 2.97 0.76 10.85 4.45 1.92 0.93

detector, and ChemStation software was used to measure the volume fractions of gas product components. The ideal gas equation was used to convert the data from a volume to a mass basis. The liquid product sample was analyzed with a simulated distillation gas chromatograph with a hydrogen flame ionization detector to determine the mass fractions of gasoline plus diesel (C5-350 °C) and heavy oil (>350 °C). The coke content on the spent catalyst was measured with a coke analyzer.

3. Results and Discussion In this work, the conversion of atmospheric residue is defined as the sum of the yields of dry gas, liquefied petroleum gas (LPG), gasoline, diesel, and coke. 3.1. Catalytic Pyrolysis of Daqing AR on Commercial CPP Catalyst. The conversion and product yields of the catalytic pyrolysis of Daqing AR on the commercial CPP catalyst are listed in Table 3. The conversion of Daqing AR was higher than 96 wt % and increased slightly with reaction temperature. This shows that the commercial CPP catalyst has good pyrolysis performance. As the reaction temperature increased from 600 to 700 °C, the yield of dry gas doubled from 17.79 to 37.25 wt %, that of LPG decreased from 40.46 to 30.28 wt %, that of gasoline plus diesel decreased by 40% from 27.89 to 16.52 wt %, and that of coke increased from 10.02 to 13.46 wt %. The main products of the catalytic pyrolysis of Daqing AR are dry gas and LPG, which is different from the product distribution of catalytic cracking, for which gasoline and diesel are desired products. Since dry gas and coke are the final products of thermal and catalytic reactions, it is expected their yields will increase with reaction temperature. However, LPG, gasoline, and diesel are the intermediate reaction products that are influenced by the extent of primary and secondary reactions. The latter increases with reaction temperature. In this case, the secondary reactions were severe enough at high temperature that they resulted in decreased yields of LPG and gasoline plus diesel. The yields of gas product components at various reaction temperatures are listed in Table 4. As the reaction temperature increased, the yields of hydrogen, methane, ethane, ethylene,

Catalytic and Thermal Pyrolysis of AR

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Table 5. Product Yields of the Catalytic Pyrolysis of Daqing AR on the Commercial FCC Catalyst, wt %

dry gas LPG gasoline + diesel heavy oil coke conversion





13.00 38.96 35.64 4.28 8.13 95.72

21.23 39.13 28.08 3.04 8.52 96.96

30.48 35.80 21.53 2.94 9.26 97.06

44.16 25.66 16.85 2.43 10.90 97.57

and carbon oxides (carbon dioxide and carbon monoxide) increased, those of propane, butane, and butylene decreased, and those of propylene and total light olefins reached maxima at 660 °C. The catalytic pyrolysis process involves catalytic cracking reactions on catalyst surfaces and thermal cracking reactions both on catalyst surfaces and in the interspaces between catalyst particles. The reactions in the catalytic pyrolysis process abide by both the carbonium ion and free radical mechanisms.3 Propylene, propane, butylene, and butane are the intermediate products formed from both the carbonium ion and free radical reactions, which can undergo secondary reactions such as hydrogen transfer, aromatization, cracking, and polymerization.15 Hydrogen, methane, ethylene, and ethane are primarily formed from thermal cracking reactions following the free radical mechanism, and they are unlikely to undergo secondary reactions. The reaction rates of both catalytic cracking and thermal cracking increase with reaction temperature. Therefore, the conversion and the yields of hydrogen, methane, ethylene, and ethane increased with reaction temperature, those of propylene reached maxima, and those of propane, butylene, and butane decreased owing to secondary reactions. 3.2. Catalytic Pyrolysis of Daqing AR on Commercial FCC Catalyst. To compare the pyrolysis performance of Daqing AR on various catalysts, we selected a commercial FCC catalyst and did experiments under the same reaction conditions. Table 5 shows the conversion and product yields of the catalytic pyrolysis of Daqing AR on the commercial FCC catalyst. The conversion of Daqing AR was greater than 95 wt % and increased slightly with reaction temperature. This shows that the commercial FCC catalyst also has good pyrolysis performance. As the reaction temperature increased, the yields of dry gas and coke increased, and those of LPG and gasoline plus diesel decreased. The pyrolysis behaviors of the commercial FCC catalyst are similar to those of the commercial CPP catalyst. Of course, there are some differences. As the reaction temperature increased from 600 to 700 °C, the yield of dry gas increased by 2.4-fold, and the extent of increase was larger than that of the commercial CPP catalyst. The extent of decrease of the yields of LPG and gasoline plus diesel on the commercial FCC catalyst was larger than that of the commercial CPP catalyst. The yield of coke on the commercial FCC catalyst was lower than that of the commercial CPP catalyst. Table 6 shows the yields of the gas product components at various reaction temperatures. As the reaction temperature increased, the yields of hydrogen, methane, ethane, ethylene, and carbon oxides increased, that of butane decreased, those of propane and butylene reached maxima at 630 °C, and those of propylene and total light olefins reached maxima at 660 °C. The experiments further explain that the pyrolysis behavior of (15) Meng, X. H.; Xu, C. M.; Gao, J. S. Secondary cracking of C4 hydrocarbons from heavy oil catalytic pyrolysis. Can. J. Chem. Eng. 2006, 84 (3), 322–327.

Table 6. Yields of the Components in Pyrolysis Gas of the Catalytic Pyrolysis of Daqing AR on the Commercial FCC Catalyst, wt %






4.88 15.84 13.44 34.16 1.43 0.30 4.10 2.29 3.25 6.43

7.16 16.94 14.22 38.32 2.73 0.59 7.08 3.67 3.36 4.60

10.79 17.47 12.97 41.23 2.62 0.76 11.29 5.01 2.81 2.55

15.77 14.79 8.22 38.77 3.52 1.22 17.21 6.45 1.78 0.88

Table 7. Product Yields of the Thermal Pyrolysis of Daqing AR on Quartz Sand, wt %

dry gas LPG gasoline + diesel heavy oil conversion





10.29 9.53 64.81 15.37 84.63

19.06 15.64 50.23 15.07 84.93

27.73 21.85 35.99 14.43 85.57

36.49 23.13 28.88 11.50 88.50

Table 8. Yields of the Components in Pyrolysis Gas of the Thermal Pyrolysis of Daqing AR on Quartz Sand, wt %






5.59 4.94 4.12 14.65 1.68 0.18 1.72 1.13 0.27 0.20

10.95 8.51 6.42 25.87 0.97 0.22 4.22 2.70 0.50 0.21

15.92 12.56 8.41 36.88 0.77 0.28 6.78 3.99 0.68 0.21

19.64 14.08 8.16 41.88 1.81 0.43 10.02 4.60 0.71 0.19

the commercial FCC catalyst is similar to that of the commercial CPP catalyst. 3.3. Thermal Pyrolysis of Daqing AR on Quartz Sand. Hydrocarbons undergo catalytic reactions accompanied by thermal reactions in the catalytic pyrolysis of heavy oil since the reaction temperature is high. Thermal pyrolysis of Daqing AR on quartz sand was investigated to study the function of thermal reactions in the catalytic pyrolysis of heavy oil. The conversion and product yields of the thermal pyrolysis of Daqing AR are listed in Table 7. The conversion of Daqing AR was greater than 84 wt % and increased with reaction temperature. As the reaction temperature increased from 600 to 700 °C, the yield of dry gas increased by 2.5-fold from 10.29 to 36.49 wt %, that of LPG increased by 1.4-fold from 9.53 to 23.13 wt %, and that of gasoline plus diesel decreased by 55% from 64.81 to 28.88 wt %. From the viewpoint of product distribution, the main products of the thermal pyrolysis at low reaction temperature (e630 °C) are gasoline and diesel, while the yield of dry gas at high reaction temperature (700 °C) is the highest. The thermal pyrolysis behaviors are different from the catalytic pyrolysis behaviors. The yield of LPG of the thermal pyrolysis increased with reaction temperature, while that of the catalytic pyrolysis decreased. The conversion of the thermal pyrolysis was lower than that of the catalytic pyrolysis, and the yield of gasoline plus diesel of the thermal pyrolysis

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Figure 2. Ethylene yield as a function of the reaction temperature on the commercial CPP and FCC catalysts and quartz sand.

Figure 4. Butylene yield as a function of the reaction temperature on the commercial CPP and FCC catalysts and quartz sand.

Figure 3. Propylene yield as a function of the reaction temperature on the commercial CPP and FCC catalysts and quartz sand.

Figure 5. Yield of total light olefins as a function of the reaction temperature on the commercial CPP and FCC catalysts and quartz sand.

was higher than that of the catalytic pyrolysis. The liquid sample of the thermal pyrolysis was viscous. The yields of the gas product components at various reaction temperatures are listed in Table 8. As the reaction temperature increased, the yields of hydrogen, methane, ethane, ethylene, propane, and propylene increased, that of butane varied slightly, and that of butylene reached a maximum at 660 °C. As the reaction temperature increased from 600 to 700 °C, the yields of dry gas, methane, ethylene, and ethane increased by 2.5-, 4.8-, 2.5-, and 3.1-fold, respectively, while those of LPG, propylene, and propane only increased by 1.4-, 1.9-, and 1.6fold, respectively. The reaction extent of the thermal pyrolysis of Daqing AR was high. The yield of total light olefins was 36.88 wt % at 660 °C and 41.88 wt % at 700 °C. 3.4. Comparison of Pyrolysis Product Distribution. Figures 2-5 show the yields of ethylene, propylene, butylene, and total light olefins of the pyrolysis of Daqing AR on the commercial CPP and FCC catalysts and quartz sand, respectively. The yields of ethylene, propylene, and total light olefins of the commercial CPP catalyst were higher than those of the commercial FCC catalyst, but the butylene yield of the commercial CPP catalyst was lower than that of the commercial FCC catalyst. This shows that the pyrolysis performance of the commercial CPP catalyst is better than that of the commercial FCC catalyst. The yields of propylene and butylene of the commercial FCC catalyst were higher than those of quartz sand. The yield of total light olefins of the commercial FCC catalyst was higher than that of quartz sand at reaction temperatures below 660 °C,

but it was lower than that of quartz sand at 700 °C. The extent of the increase of the ethylene yield of quartz sand with the reaction temperature was high. The ethylene yield of quartz sand was higher than that of the commercial CPP and FCC catalysts at reaction temperatures above 660 °C. In general, the commercial CPP catalyst has the best pyrolysis performance, since both the conversion and the yield of total light olefins were the highest. However, the gap between the yield of total light olefins of the commercial CPP catalyst and that of quartz sand became small as the reaction temperature increased. This is because the function of the carbonium ion reactions decreases with the reaction temperature and the free radical reactions become important at high reaction temperature. The olefins formed during the pyrolysis process can undergo hydrogen transfer reactions and convert to alkanes on the acidic sites of catalysts. As a result, the proportion of olefins in the product distribution decreases, and that of alkanes increases.16 The extent of hydrogen transfer reaction can be described by the hydrogen transfer coefficient, which is defined as the yield ratio of butane to butylene.16 Figure 6 shows the hydrogen transfer coefficient of Daqing AR pyrolysis on the commercial CPP and FCC catalysts and quartz sand. The hydrogen transfer coefficient of the thermal pyrolysis was below 0.05 and decreased slightly with the reaction temperature. The hydrogen transfer coefficient of the commercial CPP and FCC catalysts decreased from about 0.46 at 600 °C to around 0.11 at 700 °C. This shows that catalysts accelerate not only the cracking reaction, but also the hydrogen transfer reaction. (16) Chen, J. W. Technology and Engineering of Catalytic Cracking, 2nd ed.; China Petrochemical Press: Beijing, 2005; pp 150-159.

Catalytic and Thermal Pyrolysis of AR

Figure 6. Hydrogen transfer coefficient as a function of the reaction temperature on the commercial CPP and FCC catalysts and quartz sand.

Energy & Fuels, Vol. 23, 2009 69

Figure 8. RM value as a function of the reaction temperature on the commercial CPP and FCC catalysts and quartz sand.

are important if the RM value ranges from 0.5 to 1.5, while the free radical mechanism plays a primary role if the RM value is below 0.5.3 Figure 8 shows the RM value of Daqing AR pyrolysis on the commercial CPP and FCC catalysts and quartz sand. The RM value of the thermal pyrolysis was below 0.22 and varied slightly with the temperature. The RM value of the catalytic pyrolysis ranged from 0.6 to 1.1, explaining that both mechanisms play an important role. In addition, the RM value of the catalytic pyrolysis decreased with the reaction temperature, indicating that the function of the free radical mechanism increases with the reaction temperature. 4. Conclusions Figure 7. Isomerization coefficient as a function of the reaction temperature on the commercial CPP and FCC catalysts and quartz sand.

No matter on which catalyst, the hydrogen transfer coefficient decreased with reaction temperature. There are two reasons for this phenomenon. A high reaction temperature is not good for the hydrogen transfer reaction since it is an exothermic reaction. The function of the carbonium ion mechanism decreases, and that of the free radical mechanism increases as the reaction temperature increases, resulting in a decrease of the extent of hydrogen transfer reaction. The extent of isomerization reaction can be described by the isomerization coefficient, which is defined as the yield ratio of isobutylene to butylene.16 Figure 7 shows the isomerization coefficient of Daqing AR pyrolysis on the commercial CPP and FCC catalysts and quartz sand. The isomerization coefficient of the thermal pyrolysis was below 0.17, and that of the catalytic pyrolysis on the commercial CPP and FCC catalysts was above 0.35. This explains that the extent of isomerization reaction of the thermal pyrolysis following the free radical mechanism is low, while that of the catalytic pyrolysis is high. The isomerization coefficient of the commercial CPP catalyst decreased slightly with the reaction temperature, while that of the commercial FCC catalyst increased slightly. The reaction extent of the thermal pyrolysis above 600 °C is high according to the results of thermal pyrolysis. The reaction temperature of the catalytic pyrolysis is usually above 600 °C, so the thermal pyrolysis reaction is important in the catalytic pyrolysis. The mechanism parameter of the pyrolysis of hydrocarbons (RM) proposed by Meng3 can be used to describe the relative function of the free radical and carbonium ion mechanisms in the catalytic pyrolysis. RM is defined as the yield ratio of i-C4 to n-C4. It is reported that both the free radical and carbonium ion mechanisms

(1) The pyrolysis behaviors of the commercial CPP catalyst are similar to those of the commercial FCC catalyst. As the reaction temperature increased, the yields of dry gas and coke increased, while those of LPG and gasoline plus diesel decreased. (2) The conversion of the thermal pyrolysis of Daqing AR was greater than 84 wt % at reaction temperatures above 600 °C. The pyrolysis behaviors of quartz sand are different from those of the commercial CPP and FCC catalysts. (3) The ethylene yield of the thermal pyrolysis was higher than that of the catalytic pyrolysis at reaction temperatures above 660 °C. The yield of total light olefins of the thermal pyrolysis was 36.88 wt % at 660 °C and 41.88 wt % at 700 °C. (4) The commercial CPP catalyst showed the best pyrolysis performance and obtained the highest yield of total light olefins. The advantage of the commercial CPP catalyst to the production of light olefins decreased with the reaction temperature. (5) Both the hydrogen transfer and isomerization coefficients of the thermal pyrolysis were low, and those of the catalytic pyrolysis were high. The use of catalysts accelerates not only the cracking reaction, but also the hydrogen transfer and isomerization reactions. (6) The RM value of the catalytic pyrolysis was much higher than that of the thermal pyrolysis. Both the free radical and carbonium ion mechanisms play an important role in the catalytic pyrolysis on the commercial CPP and FCC catalysts, and the function of the free radical mechanism increases with the reaction temperature. Acknowledgment. Financial support was provided by the National Science Fund for Distinguished Young Scholars of China (Grants 20525621 and 20725620) and the Major Research Plan of the Ministry of Education of China (Grant 307008). EF8006867

Catalytic and Thermal Pyrolysis of Atmospheric Residue - Energy

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