Different Mechanisms of Coke Precursor Formation in Thermal

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Different Mechanisms of Coke Precursor Formation in Thermal Conversion and Deep Hydroprocessing of Vacuum Residue Wei Wang, Xin-heng Cai, Huandi Hou, Ming Dong, Zhongya Li, Feng Liu, Zelong Liu, Songbai Tian, and Jun Long Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.6b01488 • Publication Date (Web): 08 Sep 2016 Downloaded from http://pubs.acs.org on September 9, 2016

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Different Mechanisms of Coke Precursor Formation in Thermal Conversion and Deep Hydroprocessing of Vacuum Residue Wei Wang,* Xinheng Cai, Huandi Hou, Ming Dong, Zhongya Li, Feng Liu, Zelong Liu, Songbai Tian, and Jun Long Research Institute of Petroleum Processing, SINOPEC, Beijing 100083, China KEYWORDS Coke, Thermal Conversion, Deep Hydroprocessing, PAHs, FT-ICR MS

ABSTRACT. Coke formation during the refining of heavy oils has attracted extensive attentions due to the effects on liquid yield, catalyst deactivation, and operating period. Polycyclic aromatic hydrocarbons (PAHs) generally have the strongest tendencies to form coke during the refining processes, which are considered as coke precursors. In this work, a vacuum residue was treated by thermal conversion and deep hydroprocessing. The feedstock and products were characterized by Fourier transform ion cyclotron resonance mass spectrometry. The detailed distributions of aromatic hydrocarbons of the products behaved clear boundaries, which were described in limit lines. The slopes of the limit lines differed greatly between the two kinds of products, indicating different mechanism for the growth of PAHs. Thermal conversion and deep hydroprocessing of model compounds were also conducted. Thermal conversion products of phenanthrene and

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pyrene proved that only condensation reactions occurred at temperature of 450 oC and the aromatic rings were not ruptured. Deep hydroprocessing of pyrene revealed that the aromatic ring structures were cracked and then the smaller aromatic substrates combined together to form highly condensed aromatic rings. As a conclusion, the different mechanisms of coke precursor formation resulted in the different slopes of limit lines for thermal conversion and deep hydroprocessing products.

1. INTRODUCTION Coking is generally a severe problem in the refining processes.1-4 The formation of coke can reduce the yield of liquid products, cause catalyst deactivation, and shorten the operation period. Many efforts have been devoted to suppress the formation of coke.5-8 A clear elucidation of the mechanism of coke formation would be helpful to promote these endeavors. Coke is generally considered as a complex carbonaceous mixture with highly condensed aromatic structures. It has been characterized by many analytical techniques,9-12 such as nuclear magnetic resonance (NMR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), and Fourier transform infrared spectroscopy (FTIR). Through these studies, coke formation and deposition is related with the properties of feedstock,13,14 types of catalyst,15,16 operating condition,17-20 and phase separation.13,21 However, the detailed chemical identity of coke structure is still limited due to the complexity, poor solubility, and low volatility. Polycyclic aromatic hydrocarbons (PAHs) are considered as coke precursors,22-25 and the growth of aromatic rings provide important information of coke formation. The structures of


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PAHs in petroleum samples after visbreaking26,27 and hydrocracking28,29 have been widely studied by mass spectrometry. Series of fused PAHs with more than 6 rings have been found in the products, which are valuable for understanding the coke formation pathways during the refining processes. The behaviors of model compounds have also been studied. Only thermal polymerization of pyrene was observed during heating at 480 oC in nitrogen flow.30 Both cracking and addition products were detected in the thermal cracking of alkyl-PAHs and archipelago model compounds.31,32 Hydrocracking of pyrene generally resulted in gas, liquid, and coke products, while most former reports focused on the light products which were measured by gas chromatography-mass spectrometer (GC-MS).33-35 With the development of Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS), more details about the transformation of aromatic hydrocarbons in petroleum samples can be obtained during the refining processes.36-38 It was noticed that some highly condensed aromatic hydrocarbons without side-chains appeared after deep hydroconversion of asphaltene.37 The relationship between the carbon number and double bond equivalence (DBE) of these highly condensed aromatic hydrocarbons led to the concept of PAH planar limit,39,40 which was also used to describe the structure differences of petroleum fractions.41 In this work, a vacuum residue (VR) was treated by thermal conversion and deep hydroprocessing. The VR feedstock and products were characterized by atmospheric pressure photoionization (APPI) FT-ICR MS. Clear boundaries were observed for the distribution of aromatic hydrocarbons of the products, but the slopes of the limit lines were quite different for thermal conversion and deep hydroprocessing. This result indicated the growth mechanism of PAHs may be not the same for different processes. In order to clarify the mechanism, experiments with model compounds were also conducted at different conditions. Polymerization


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of phenanthrene and pyrene at thermal conversion was observed at temperature of 450 oC. The products of pyrene after hydroprocessing was much more complex and the structures of some heavy products were more condensed than those of thermal conversion products. Two different growth mechanisms of PAHs were suggested according to the structure characteristics of the thermal conversion and deep hydroprocessing products.

2. EXPERIMENTAL SECTION Chemicals. A vacuum residue (VR) sample from Tahe crude oil in northwest of China was served as the feedstock. The boiling range of the VR feedstock was above 540 oC. The sulfur and nitrogen content of the VR feedstock was 3.45% and 0.77%, respectively. Model compounds phenanthrene and pyrene were purchased from J&K Scientific Ltd. and the purity was 98%. Thermal Conversion Reactions. Thermal conversions of VR feedstock and model compounds were performed in microreactors (250 mL) at atmospheric pressure. Approximately 100 g of the VR feedstock was heated at 410 oC for 90 min and protected by nitrogen gas flow. For model compounds, more severe conditions were required. Approximately 25 g of phenanthrene or pyrene was heated at 450 oC for 10 h in nitrogen gas flow. The reactor was cooled in ice water after thermal reactions to avoid further reactions. About 35% of solid product was toluene soluble for VR. The recovery yields of the model compounds were above 90%, and almost 100% of the solid products could be dissolved in toluene at present condition. Deep Hydroprocessing Reactions. Deep hydroprocessing of VR feedstock and model compound pyrene were conducted in microreactors (1000 mL). Approximately 300 g of VR feedstock and 1.8 g of Al2O3-supported Fe−Mo catalyst were introduced to the reactor. The catalyst was pre-sulfided by CS2 and the size of the particles was 50~100 µm. The reactor stirrer speed was 500 rpm. The initial pressure of the reactor was 9.0 MPa with hydrogen. The pressure


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increased to an average value of 17.5 MPa under the reaction temperature of 410 oC. The pressure reduced smoothly during the reaction and the final pressure was 7.0 MPa when the reactor was cooled to room temperature. The reaction period was about 3 h. More severe condition was also required for model compound pyrene, such as better catalyst, higher temperature, and lower initial pressure of hydrogen. Approximately 36 g of pyrene, 54 g of toluene, and 10 g of catalyst were introduced to the reactor. The catalyst was NiO/WO3 supported on alumina which was pre-sulfided by CS2. The size of the catalyst was 200 µm. The operating temperature of pyrene was 420 oC. The reactor stirrer speed was 500 rpm. The initial pressure of hydrogen was 5.0 MPa. The pressure increased to an average value of 11.7 MPa under the reaction temperature and the final pressure was 3.6 MPa when the reactor was cooled to room temperature. The reaction of pyrene lasted for about 6 h. FT-ICR MS Analysis. VR feedstock, thermal conversion product of VR, and deep hydroprocessing product of VR were dissolved in toluene and diluted to 0.5 mg/mL. Thermal conversion and deep hydroprocessing products of model compounds were dissolved in toluene and diluted to 0.01 mg/mL. The prepared samples flowed through a fused-silica capillary at a rate of 360 µL/h by a syringe pump (Hamilton Corp.). Analyses were conducted on a 9.4 T Bruker Apex FT-ICR MS. Positive mode atmospheric pressure photoionization (APPI) was used as the ionization source. Nitrogen served as the drying gas and nebulizing gas. The drying gas flow rate was 4.0 L/min at the temperature of 200 oC. The nebulizing gas flow rate was 1.0 L/min and the APPI temperature was 400 oC. The skimmer voltage was set to 30.0 V. The m/z range was from 250 to 1500 Da for VR and its products, while the m/z range was from 150 to 1000 Da for the products of model compounds. The data size was 4M and time-domain data sets were 256 scans.


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Mass Calibration and Data Analysis. The APPI FT-ICR MS spectra were externally calibrated by Tuning Mix (Agilent Corp.). The peaks with a relative abundance greater than six standard deviations of baseline rms noise (6σ) were chosen for the data analysis. Chemical formulas of the peaks (CcHhNnOoSs) were calculated according to the m/z values within ±1 ppm. GC-MS Analysis. Deep hydroprocessing product of pyrene was analyzed on an Agilent 7890A gas chromatograph and 5977C mass detector with a HP-5MS column (30 m × 0.25 mm × 0.25 µm). Liquid injection of 0.5 µL was introduced into the injector at 300 oC with a 20:1 split ratio. The temperature program of GC oven is 50 oC for 5 min, 5 oC/min to 300 oC, and 300 oC for 10 min. The temperature of ion source was 230 oC. The mass detector was scanned from 30 to 500 Da.

3. RESULTS AND DISCUSSION 3.1 Thermal Conversion and Deep Hydroprocessing of VR Feedstock. DBE versus Carbon number distributions of aromatic hydrocarbon compounds in VR feedstock, thermal conversion product of VR, and deep hydroprocessing product of VR are shown in Figure 1. The size of the bubble indicates the relative abundance of the compound. The carbon number distribution varies from 30 to 80 for the VR feed, while the distribution of DBE is from 4 to 31 and the center of DBE is around 10 to 15. The ranges of carbon number distributions reduce to 20~60 for thermal conversion product and 30~70 for deep hydroprocessing product, while the DBE expands to higher than 36 for both products. The shorten carbon number of the products indicate the cracking of side chains after thermal conversion and deep hydroprocessing. Moreover, the centers of DBE shift to much higher value for both products, revealing the dramatic growth of aromatic rings.


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It is also noted that the hydrocarbon distributions of VR feed and its products are below the limit line of DBE = 0.9*(Carbon Number), which is the absolute upper limit of hydrocarbon compositional space for fossil oils.39 Clear boundaries of VR feed and its products are also observed. For hydrocarbon distributions of VR feed, the slope of the limit line of the boundary is 0.6991, which is determined by the structure characteristic of PAHs in the feedstock. However, the slope of limit line of the boundary is 0.7630 for thermal conversion product and 0.9482 for deep hydroprocessing product, respectively. The differences of the slopes indicate that the structures of PAHs in the products may be also different.41 To find out the structure differences, thermal conversion and deep hydroprocessing reactions are applied to model compounds. 3.2 Thermal Conversion of Phenanthrene and Pyrene. The APPI FT-ICR MS spectra of thermal conversion products of phenanthrene and pyrene are shown in Figures 2 and 3. Some probable structures are labelled to the mass peaks according to the molecular formulas. Although isomers of the products are not considered,30,42 these structures can still reveal some useful information. The thermal conversion products of model compounds are relatively simple and regular. The products are mainly in the form of dimer, trimer, tetramer and so on. The starting molecules are linked by single bonds or ring structures through free-radical chain reactions.43,44 The cracking of the aromatic rings of model compounds is not observed during thermal conversion at 450 oC. The DBE versus carbon number distributions of the thermal conversion products are shown in Figures 4 and 5. Two possible pathways are suggested: The starting molecules are just linked by single bonds for path A, while the starting molecules are only linked by ring structures for path B. The bubbles of the products locate between the fitted lines of path A and path B. The position of the bubbles can be seen more clearly in Figure S1 without considering the relative abundance of


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the thermal conversion products. As a result, the formation of thermal conversion products is considered as a mixture of path A and path B, and the slopes of the products are also between the slopes of path A and path B. Moreover, the slopes of path A and path B are determined by equations 1 and 2 (Detailed discussions can be found in the Supporting Information) SlopeA = DBE0 / C0 SlopeB = (DBE0 + 1) / C0

(1) (2)

Where DBE0 is DBE of the starting molecule and C0 is carbon number of the starting molecule. The relationship between the structure of PAHs starting molecule and slopeA/slopeB is listed in Table 1. It can be found clearly that more condensed aromatic ring structures will result in higher slopeA and slopeB. As the center of DBE is from 10 to 15 for the VR feedstock studied here, it is reasonable that the slope increases to a value of 0.7630 for the thermal conversion product according to Table 1. The reactions during coke formation are very complex for VR feedstock. However, the limit line of the product provides a clear boundary for these reactions and the slope of the limit line reveals important information about how aromatic rings grow to larger PAHs. Several factors are not included here to simplify the discussion. First, the conversion from saturated hydrocarbons to PAHs is not considered,45 as this is not the main reactions at present condition. In fact, the saturate fractions of VR increase from 8.6% to 21.7% after thermal conversion. Second, the starting molecules with side chains are not considered, as thermal treating may cause cleavage of long aliphatic side chains46 and products of PAHs with short side chains are more close to the limit line. At last, the reactions between different starting molecules are not considered, although intermolecular reactions are more accordant with the situation of complex oil samples. However, it can be proved that the slope of mixed starting molecules is just


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between the slopes of single starting molecules. For example, if there are two starting molecules mixed together, then slopeA and slopeB of the products can be described in equations 3 and 4 (Detailed discussions can be found in the Supporting Information) SlopeA of the mixed products = (n1DBE1 + n2DBE2) / (n1C1 + n2C2)

(3)

SlopeB of the mixed products = (n1DBE1 + n2DBE2 + n1+ n2) / (n1C1 + n2C2)

(4)

Where n1 and n2 are the mole fractions of starting molecules 1 and 2, DBE1 and DBE2 are DBEs of the starting molecules 1 and 2, and C1 and C2 are carbon numbers of the starting molecules 1 and 2. It can be easily proved that the slope of the mixed products is between the slopes of single starting molecule. As a result, the distribution of mixed products is still below the upper limit line of single starting molecule. 3.3 Deep Hydroprocessing of Pyrene. The products of pyrene after deep hydroprocessing have been measured by GC-MS and FT-ICR MS, as shown in Figures 6 and 7. The products are much more complex than thermal conversion products of model compounds. The hydrogenation and cracking of pyrene are confirmed by both GC-MS and FT-ICR MS, which is consistent with former reports.47-49 Some heavy products are also found by FT-ICR MS, which can be divided into three types as labelled in Figure 7. Type I compounds indicate that the solvent toluene may be also involved in the reactions.50 Type II compounds are mainly formed through the linkage of pyrene, hydrogenated pyrene, and methylated pyrene, which are very similar to the thermal conversion products. The existence of these compounds reveals that free-radical chain reactions could not be totally avoided at present hydroprocessing condition. However, the relatively low abundance of trimer and the absence of tetramer prove that the free-radical chain reactions are strongly suppressed at present condition. Type III compounds contain more condensed aromatic ring structures than type I and type II compounds. These highly condensed PAHs could not be


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formed just by the linkage of pyrene or hydrogenated pyrene. In order to form type III compounds, the ring structure of pyrene has to be ruptured and then the generated small aromatic molecules would combine together as shown in Scheme 1.51 A proposed mechanism of coke precursor formation during deep hydroprocessing is illustrated in Figure 8 according to above discussions. Compounds C24H12, C32H14, and C40H16 are chosen to generate the limit line for deep hydroprocessing. The reason is that these compounds have similar structures with type III compounds and have been widely found in hydroprocessing products of petroleum samples.28,37 The DBE versus carbon number distributions of the hydroprocessing product of pyrene is also shown in Figure 8. It can be found clearly that all of the products are below the limit line and type III compounds are very close to the limit line. It is also noted that the slope of the limit line for deep hydroprocessing is 0.8750, which is significantly higher than the slope of thermal conversion products. This result explains why the slopes of limit lines are different for thermal conversion and deep hydroprocessing products of the VR feedstock.

4. CONCLUSIONS In this work, a vacuum residue was treated by thermal conversion and deep hydroprocessing. Clear boundaries were observed in DBE versus carbon number distributions of aromatic hydrocarbons of the products. These boundaries were described in limit lines and the different slopes of the limit lines indicated different structures of PAHs formed in the products. To study the growth mechanisms of PAHs at different conditions, model compounds were also treated by thermal conversion and deep hydroprocessing. Thermal conversion products of phenanthrene and pyrene revealed that the aromatic ring structures kept unchanged and only condensation reactions of the starting molecules occurred at temperature of 450 oC. The starting


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molecules were linked together by single bonds or rings. The slopes of the limit lines of thermal conversion products were related with the structures of the starting molecules. The deep hydroprocessing product of pyrene was quite different from thermal conversion. The aromatic rings of pyrene were hydrogenated and then cracked into small PAHs molecules. These fragment PAHs molecules combined together to generate a more condensed aromatic structure than the products of thermal conversion. As a result, the slope of the limit line of deep hydroprocessing product is much higher than the slope of thermal conversion product. These results may be helpful for understanding of coke formation mechanisms in different refining processes.


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Figure 1. The DBE versus carbon number distributions of vacuum residue feedstock and the products of thermal conversion and deep hydroprocessing.

Figure 2. APPI FT-ICR MS spectrum of thermal conversion product of phenanthrene at 450 oC. The molecular structures labelled to the mass peaks are just shown as illustrations. The exact structures or other isomers are not considered here.


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Figure 3. APPI FT-ICR MS spectrum of thermal conversion product of pyrene at 450 oC. The molecular structures labelled to the mass peaks are just shown as illustrations. The exact structures or other isomers are not considered here.

Figure 4. The DBE versus carbon number distribution of thermal conversion product of phenanthrene at 450 oC. The red circle represents the position of phenanthrene. Limit lines A and B are determined by ideal products through path A and path B.


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Figure 5. The DBE versus carbon number distribution of thermal conversion product of pyrene at 450 oC. The red circle represents the position of pyrene. Limit lines A and B are determined by ideal products through path A and path B.

Figure 6. Gas chromatogram of deep hydroprocessing product of pyrene. The peaks are identified by mass spectrometry and the isomers of methylated PAHs are not distinguished. C12H14O4 is an impurity of the solvent.


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Figure 7. APPI FT-ICR MS spectrum of deep hydroprocessing product of pyrene. The molecular structures labelled to the mass peaks are just shown as illustrations. The exact structures or other isomers are not considered here.

Scheme 1


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Figure 8. The DBE versus carbon number distribution of deep hydroprocessing product of pyrene. The red circle represents the position of pyrene. A possible pathway to generate the limit line is also suggested.


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Table 1. The relationship between the structures of starting molecules and slopeA/slopeB

C0

DBE0

SlopeA

SlopeB

10

7

0.7000

0.8000

12

8

0.6667

0.7500

14

10

0.7143

0.7857

16

12

0.7500

0.8125

18

13

0.7222

0.7778

24

19

0.7917

0.8333

32

26

0.8125

0.8438

40

33

0.8250

0.8500

54

46

0.8519

0.8704


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ASSOCIATED CONTENT Supporting Information. Additional information as noted in text. This material is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Author * E-mail: [email protected]. Notes The authors declare no competing financial interest. ACKNOWLEDGMENT This work was supported by Major State Basic Research Development Program of China (973 Program, No. 2012CB224801). ABBREVIATIONS PAHs, Polycyclic aromatic hydrocarbons; APPI, Atmospheric pressure photoionization; FT-ICR MS, Fourier transform ion cyclotron resonance mass spectrometry; DBE, Double bond equivalence; VR, Vacuum residue. REFERENCES (1)

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(21) Ali, F. A.; Hauser, A.; Abdullah, H. A.; Al-Adwani, A. Energy Fuels 2006, 20, 45-53. (22) Guisnet, M.; Magnoux, P. Appl. Catal. A: Gen. 2001, 212, 83-96. (23) Gentzis, T.; Rahimi, P. M. Fuel 2003, 82, 1531-1540. (24) Wang, G.; Eser, S. Energy Fuels 2007, 21, 3563-3572. (25) Castano, P.; Gutierrez, A.; Hita, I.; Arandes, J. M.; Aguayo, A. T.; Bilbao, J. Energy Fuels 2012, 26, 1509-1519. (26) Ogbuneke, K. U.; Snape, C. E.; Andresen, J. M.; Crozier, S.; Russell, C.; Sharpe, R. Energy Fuels 2009, 23, 2157-2163. (27) Flego, C.; Zannoni, C. Energy Fuels 2010, 24, 6041-6053. (28) Qian, K.; Edwards, K. E.; Siskin, M. Energy Fuels 2001, 15, 949-954. (29) Fetzer, J. C. Polycyclic Aromat. Compd. 2007, 27, 143-162. (30) Esguerra, D. F.; Hoffman, W. P.; Thies, M. C. Fuel 2014, 124, 133-140. (31) Alshareef, A. H.; Scherer, A.; Tan, X.; Azyat, K.; Stryker, J. M.; Tykwinski, R. R.; Gray, M. R. Energy Fuels 2011, 25, 2130-2136. (32) Alshareef, A. H.; Scherer, A.; Tan, X.; Azyat, K.; Stryker, J. M.; Tykwinski, R. R.; Gray, M. R. Energy Fuels 2012, 26, 1828-1843. (33) Haynes, H. W. Jr.; Parcher, J. F.; Helmer, N. E. Ind. Eng. Chem. Process Des. Dev. 1983, 22, 401-409. (34) Matsui, H.; Akagi, K.; Murata, S.; Nomura, M. Energy Fuels 1995, 9, 435-438. (35) Isoda, T.; Maemoto, S.; Kusakabe, K.; Morooka, S. Energy Fuels 1999, 13, 617-623. (36) Schaub, T. M.; Rodgers, R. P.; Marshall, A. G.; Qian, K.; Green, L. A.; Olmstead, W. N. Energy Fuels 2005, 19, 1566-1573.


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(37) Purcell, J. M.; Merdrignac, I.; Rodgers, R. P.; Marshall, A. G.; Gauthier, T.; Guibard, I. Energy Fuels 2010, 24, 2257-2265. (38) Diao, R.; Wang, W.; Wang, N.; Liu, Z.; Dai, L.; Tian, S. China Pet. Process Pe. 2012, 14, 80-88. (39) Hsu, C. S.; Lobodin, V. V.; Rodgers, R. P.; McKenna, A. M.; Marshall, A. G. Energy Fuels 2011, 25, 2174-2178. (40) Podgorski, D. C.; Corilo, Y. E.; Nyadong, L.; Lobodin, V. V.; Bythell, B. J.; Robbins, W. K. McKenna, A. M.; Marshall, A. G.; Rodgers, R. P. Energy Fuels 2013, 27, 1268-1276. (41) Cho, Y.; Kim, Y. H.; Kim, S. Anal. Chem. 2011, 83, 6068-6073. (42) Mulholland, J. A.; Mukherjee, J.; Sarofim, A. F. Energy Fuels 1997, 11, 392-395. (43) Reyniers, G. C.; Froment, G. F.; Kopinke, F. D.; Zimmermann, G. Ind. Eng. Chem. Res. 1994, 33, 2584-2590. (44) Tian, L.; Shen, B.; Liu, J. Energy Fuels 2012, 26, 1715-1724. (45) Kim, J.; Park, S. H.; Lee, C. H.; Chun, B. H.; Han, J. S.; Jeong, B. H.; Kim, S. H. Energy Fuels 2012, 26, 5121-5134. (46) Chiaberge, S.; Guglielmetti, G.; Montanari, L.; Salvalaggio, M.; Santolini, L.; Spera, S.; Cesti, P. Energy Fuels 2009, 23, 4486-4495. (47) Minabe, M.; Nakada, K. Bull. Chem. Soc. Jpn. 1985, 58, 1962-1966. (48) Korre, S. C.; Klein, M. T.; Quann, R. J. Ind. Eng. Chem. Res. 1995, 34, 101-117. (49) Sasaki, M.; Song, C.; Plummer, M. A. Fuel 2000, 79, 295-303. (50) Esguerra, D. F.; Hoffman, W. P.; Thies, M. C. J. Supercrit. Fluids 2013, 79, 170-176. (51) McClaine, J. W.; Wornat, M. J. J. Phys. Chem. C 2007, 111, 86-95.


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Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 1. The DBE versus carbon number distributions of vacuum residue feedstock and the products of thermal conversion and deep hydroprocessing. 119x62mm (300 x 300 DPI)


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Energy & Fuels

Figure 2. APPI FT-ICR MS spectrum of thermal conversion product of phenanthrene at 450 oC. The molecular structures labelled to the mass peaks are just shown as illustrations. The exact structures or other isomers are not considered here. 119x57mm (300 x 300 DPI)


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 3. APPI FT-ICR MS spectrum of thermal conversion product of pyrene at 450 oC. The molecular structures labelled to the mass peaks are just shown as illustrations. The exact structures or other isomers are not considered here. 119x60mm (300 x 300 DPI)


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Energy & Fuels

Figure 4. The DBE versus carbon number distribution of thermal conversion product of phenanthrene at 450 oC. The red circle represents the position of phenanthrene. Limit lines A and B are determined by ideal products through routes A and B. 119x39mm (300 x 300 DPI)


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 5. The DBE versus carbon number distribution of thermal conversion product of pyrene at 450 oC. The red circle represents the position of pyrene. Limit lines A and B are determined by ideal products through routes A and B. 119x41mm (300 x 300 DPI)


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Energy & Fuels

Figure 6. Gas chromatogram of deep hydroprocessing product of pyrene. The peaks are identified by mass spectrometry and the isomers of methylated PAHs are not distinguished. C12H14O4 is an impurity of the solvent. 119x67mm (300 x 300 DPI)


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 7. APPI FT-ICR MS spectrum of deep hydroprocessing product of pyrene. The molecular structures labelled to the mass peaks are just shown as illustrations. The exact structures or other isomers are not considered here. 119x68mm (300 x 300 DPI)


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Energy & Fuels

Figure 8. The DBE versus carbon number distribution of deep hydroprocessing product of pyrene. The red circle represents the position of pyrene. A possible route to generate the limit line is also suggested. 119x83mm (300 x 300 DPI)


Energy & Fuels

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Scheme 1 119x48mm (300 x 300 DPI)


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Different Mechanisms of Coke Precursor Formation in Thermal

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