Transformation of Petroporphyrins-Enriched Subfractions from

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Transformation of Petroporphyrins-Enriched Subfractions from Atmospheric Residue during Noncatalytic Thermal Process under Hydrogen by Positive-Ion Electrospray Ionization FT-ICR Mass Spectrometry He Liu, Jun Mu, Zongxian Wang,* Aijun Guo,* and Kun Chen State Key Laboratory of Heavy Oil Processing, College of Chemical Engineering, China University of Petroleum (East China), 66 Changjiang West Road, Qingdao Economic Development Zone, Qingdao Shandong 266580, China ABSTRACT: Nickel and vanadyl porphyrins were separated from atmospheric residue of Canadian oil sand bitumen by solvent extraction and column chromatography and then subjected to noncatalytic thermal process under hydrogen. The petroporphyrins before and after thermal process were characterized by UV−vis spectroscopy and positive-ion electrospray ionization FT-ICR mass spectroscopy to probe their structural transformation. Three main vanadyl porphyrins, including N4VO, N4VOS, and N4VO2 and a fraction of N5VO2 are identified in the feed fraction. With time increasing, the relative abundance of CnH2n−28N4VO (DBE = 17) increases initially and then decreases, in contrast with CnH2n−26N4VO (DBE = 18). It suggests the hydrogenation and rapid hydrogenolysis of petroporphyrins. The carbon number shifts to the lower mass range with increased process severity, indicating extensive thermal cracking reactions of petroporphyrins have occurred. N4VOS porphyrins show very similar variation of DBE and carbon number distribution as N4VO. A considerable proportion of new types of N4VO2, N4VO3 and N5VO2 are identified in the product after 30 min by accurate mass measurement and isotopic distribution. Under more severe conditions, these new species gradually diminish. It is inferred that the new species could most possibly derive from disassociation of large molecules in addition to chemical transformation. H2S and high hydrogen pressure could promote the hydrogenation of petroporphyrins. H2S can also enhance their thermal cracking reaction while high hydrogen pressure inhibits it. Nickel porphyrins present almost the same phenomena with vanadyl porphyrins, though with low content. Analysis of the petroporphyrins at the molecular level reveals their behavior and transformation during thermal process under hydrogen and could also benefit the catalysts design in HDM process.

1. INTRODUCTION With the supply of conventional crude oil decreases all over the world, processing of heavy crude oil and heavy residue distillates has become a hot spot in refineries.1 It is wellknown that these heavy oils are abundant with nickel and vanadium.2 These metals could cause catalysts deactivation during catalytic process and promote condensation reactions to form coke during noncatalytic thermal process,3,4 which stimulates research efforts aimed at finding ways to remove these contaminants.2 Preliminary studies on transformation of these metal compounds at molecular level would be helpful for better understanding of their fate and essential effect on the hydroconversion process in order to develop more effective demetallization process. A considerable part of nickel and vanadium is present as metalloporphyrins.2 A number of studies on transformation of metalloporphyrins during catalytic hydroconversion in terms of mechanism, kinetics, and final deposits have been carried out by model compounds.5−8 The real petroporphyrins are of complicated structures in complex oil matrix and could vary significantly from model compounds in the transformation behavior. Several researchers have also attempted to probe their transformations using heavy oil system. Miller et al. 9 characterized the nonporphyrin nickel and vanadium in feed residue and hydrocracked products enriched with metals by Xray absorption fine structure spectroscopy (XAFS). Little © XXXX American Chemical Society

change of the local coordination of these metals was found in hydrocracked residuum. No characteristic vanadyl porphyrin absorptions were observed by Kekalainen et al.10 in the hydrocracking product oil. Electron paramagnetic resonance (EPR) of vanadyl porphyrins in oil has been widely studied and is sensitive to transformation of the surrounding hydrogen and nitrogen.3,11−14 Recently, Tayeb et al.15 compared the pulsed EPR spectra of vanadyl porphyrins in asphaltenes before and after hydroprocessing. They also proposed that pulsed EPR could be used in more hydroconverted effluents to probe the evolution of electronic structure of vanadyl porphyrins. It needs further work to do and EPR is not applicable for nickel porphyrins. It can be seen that great challenges are still in the limited characterization methods for such low concentration of metals and high reactivity of metal compounds during hydrodemetallization (HDM).16 Isolation and purification for petroporphyrins could greatly facilitate their characterization.17−19 Fournier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) has been proved to be an efficient method for characterizing metalloporphyrins at molecular level because of its ultrahigh resolution.20−23 Recently, Liu et al.16 separated the vanadyl porphyrins from petroleum vacuum Received: October 28, 2015 Revised: January 26, 2016

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DOI: 10.1021/acs.energyfuels.5b02550 Energy Fuels XXXX, XXX, XXX−XXX

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ionization efficiency. The sample solution was infused via an Apollo II electrospray source at 3 μL/min using a syringe pump. The conditions for positive-ion formation were −4.0 kV emitter voltage, −4.5 kV capillary column introduced voltage, and 320 V capillary column end voltage. Ions accumulated for 0.1 s in a hexapole with 2.4 V direct current and 500 Vp−p radio frequency (RF) amplitude. An argon-filled hexapole collision cell was operated at 5 MHz and 700 Vp−p RF amplitude, in which ions accumulated for 0.6 s. The extraction period for ions from the hexapole to the ICR cell was set to 1.5 ms. The RF excitation was attenuated at 11.75 dB and used to excite ions over the range of 200−1000 Da. Data sets (4M) were acquired, and 128 scans were coadded to enhance the signal-to-noise ratio and dynamic range. FT-ICR MS was internally calibrated using [CnH2n−17N1 + H]+ and [CnH2n−19N1 + H]+ of high relative abundance in the standard oil. Internal quadratic calibration was also performed. The typical mass resolving power, m/Δm50% > 600 000, at m/z 400 with 0.4 ppm mass error, was achieved. Peaks with a relative abundance greater than 6 times the standard deviation of the baseline noise level were exported to a spreadsheet. The detail has been reported elsewhere.27

residua before and after HDM and successfully characterized their structures by FT-ICR MS. However, the detected vanadyl porphyrins depend a lot on the extraction method. Only the most abundant species can be found in the product. Thermal treatment directly to the separated petroporphyrins could reduce the influence of extraction method to some extent. During noncatalytic hydroconversion process, these metal compounds are exposed to complex atmospheres. Their demetallization reactions could occur with a low demetallization activity, which may also facilitate the identification of petroporphyrins. According to the available articles, transformation of petroporphyrins during noncatalytic thermal process under hydrogen is sporadically involved. Bonné et al.24 studied the kinetics by model compounds under mild conditions. Rankel25 has studied the degradation of petroporphyrins in heavy residue when exposed to heat, air, hydrogen, and hydrogen sulfide by UV−vis spectroscopy, but only the quantitative conversion is obtained. Much more work need to be done to recognize the transformation of petroporphyrins during noncatalytic thermal process under hydrogen. In this work, the nickel and vanadyl porphyrins from atmospheric residue of Canadian oil sand bitumen were separated by solvent extraction combined with column chromatography and then subjected to thermal process under hydrogen. The petroporphyrins before and after thermal process were characterized by FT-ICR MS. The transformation of these petroporphyrins was traced at a molecular level. Effects of the reaction time, reaction atmosphere, and hydrogen pressure on transformation of vanadyl porphyrins were also systematically investigated.

3. RESULTS AND DISCUSSION 3.1. UV−vis Spectroscopy Analysis. Figure 1 shows the UV−vis spectra of FV and FNi from OSAR and their products after noncatalytic thermal process under hydrogen for 30, 60, and 120 min. The characteristic absorptions of vanadyl porphyrins at 530 and 570 nm and nickel porphyrins at 550

2. EXPERIMENTAL SECTION 2.1. Sample Preparation. Atmospheric residue from Canadian oil sand bitumen (OSAR, Ni: 80 ppm, V: 190 ppm) was selected as the feedstock. The amount of elemental sulfur and nitrogen in OSAR is 3.97 and 0.5 wt %, respectively. Petroporphyrins were obtained from the feed residue by solvent extraction followed by silica gel chromatographic separation, which has been described in previous work.26,27 Briefly, the feed oil was first extracted by acetonitrile and then separated into six subfractions on silica gel chromatographic column eluted by sequential solvents with increasing polarity. The subfractions showing characteristic UV−vis absorptions of metalloporphyrins have been labeled as nickel porphyrins subfraction (FNi) and vanadyl porphyrins subfraction (FV).27 For comparison, nickel porphyrins from atmospheric residue of Chinese Liaohe heavy oil (LHAR) were also obtained. The properties of LHAR have been reported previously.27 2.2. Microautoclave Experiment. About 0.01 g of petroporphyrins was weighted accurately with a precision of ±0.001 g into a glass tube and then loaded into a 25 mL stainless steel autoclave. After purged with hydrogen to ensure oxygen-free atmosphere, the reactor was subsequently charged with hydrogen. Then, it was preheated in a tin-bathed heater at about 300 °C within 2 min and immediately plunged into another tin-bathed heater at 380 °C for varying reaction times. The reaction was quenched by immersing the reactor in cold water. The final products were completely recovered using methylene dichloride and then analyzed by UV−vis spectroscopy and mass spectroscopy. 2.3. Analysis Methods. UV−vis spectroscopy measurement was completed on Varian Cary 50 spectrophotometer with scanning range falling between 700 and 200 nm. ESI FT-ICR MS analysis was completed on Bruker apex-ultra FT-ICR MS equipped with a 9.4 T actively shielded superconducting magnet. The analysis method and data processing have been reported previously.18 A total of 10 mg of sample were diluted with 1 mL of toluene/methanol (1:1, v/v) solution, and 5 μL of formic acid was added to enhance the ESI

Figure 1. UV−vis spectra of the feed petroporphyrins-enriched subfractions from OSAR and products under different reaction times (380 °C, 5 MPa). (a) FV, (b) FNi. B


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Energy & Fuels nm gradually decrease with time increasing. A new absorption at 630 nm is observed in the spectra of products for vanadyl porphyrins. According to the report of Bonné et al.,24 it could be assigned to metal chlorin, suggesting the hydrogenation of vanadyl porphyrins. The chlorin is not found in the products for nickel porphyrins, possibly because of the low concentration that could not be detected by UV−vis spectroscopy. Rankel et al.25 found that about 50% of metalloporphyrins was converted in the autoclave experiment at 400 °C under hydrogen without catalysts. In our previous work,28 noncatalytic conversions of metal octaethylporphyrins and metal tetraphenylporphyrins at 380 °C under hydrogen atmosphere for 30 min were about 15% and 35%, respectively. For the real petroporphyrinenriched subfractions, the absorption at 570 nm characteristic of vanadyl porphyrins decreases by about 28% at 30 min, while that at 550 nm characteristic of nickel porphyrins decreases by about 12%. As noted by researchers,18 the absorption of petroporphyrins in UV−vis spectrum could be affected by many factors, such as the association of large molecules and types of solvents, etc. Therefore, decrease of the characteristic absorption could not all account for conversion of petroporphyrins in real oil fraction. A more detailed structural characterization is needed to better understand the transformation of petroporphyrins. 3.2. Transformation of N4VO and N4VOS Porphyrins by Positive-Ion ESI FT-ICR MS. Figure 2 shows the positive-

Figure 3. DBE distribution of the feed FV and products under different reaction times (380 °C, 5 MPa). (a) N4VO, (b) N4VOS.

shifts from 18 to 17, indicating the hydrogenation of vanadyl porphyrins. Meanwhile, N4VO species with DBE of 16 are also observed after thermal process for longer times, as shown in the expanded mass spectra at m/z 546 (Figure 2). This can be attributed to the formation of hydrogenated intermediates of vanadyl porphyrins that have been detected by UV−vis spectroscopy. Spectral evidence of hydrogenated intermediates for petroporphyrins in real oil system were rarely reported previously. Additionally, N4VO species with DBE 26 and 27 are also detected in the product under severe conditions. Based on the possible structures of N4VO porphyrins proposed by Qian et al.,21 they can be chemically converted from other types of N4VO by benzene increment. The variation plot of relative abundance of N4VO with different DBE values versus reaction time is inserted in Figure 3a. It has been reported that metalloporphyrins with higher DBE tend to present a higher reactivity.6,28 This results in the increase of relative abundance of types with lower DBE. The relative abundance of CnH2n−28N4VO (DBE = 17) increases initially and then decreases, in contrast with CnH2n−26N4VO (DBE = 18). It suggests that N4VO porphyrins are subjected to hydrogenation and subsequent rapid hydrogenolysis reactions. At the late stage, equilibrium seems to be present between relative abundance of CnH2n−28N4VO and CnH2n−26N4VO.

Figure 2. Broadband and expanded positive-ion ESI FT-ICR MS spectra of the feed FV and products under different reaction times (380 °C, 5 MPa).

ion ESI FT-ICR MS spectra of FV before and after thermal process under hydrogen for different reaction times. The center of the spectrum gradually shifts to a lower molecular mass range as time increases. Consistent with UV−vis analysis, abundant characteristic vanadyl porphyrins peaks are revealed in MS spectra. The main V compounds in the feed FV have been discussed in detail in our previous work, including N4VO, N4VO2, and N4VOS porphyrins.27 Figure 3a shows DBE distribution for N4VO porphyrins based on the ESI FT-ICR mass analysis. In the feed FV, three more types of N4VO porphyrins with DBE of 23, 24, and 25 are identified, in addition to the well-documented six types, i.e., ETIO (DBE = 17), DPEP (DBE = 18), Rhodo-ETIO (DBE = 19), Rhodo-DPEP (DBE = 20), Di-DPEP (DBE = 21), Rhododi-DPEP (DBE = 22). The most abundant N4VO species are DPEP types. After thermal treatment, the dominant DBE value C


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Energy & Fuels For the detected N4VOS porphyrins in the feed FV, their DBE values range from 20 to 27. The most abundant types have DBE of 23 and 24. Sulfur is typically believed to present as benzothiophene in their structures. The DBE distribution for N4VOS porphyrins in FV before and after thermal process is presented in Figure 3b. No hydrogenated species with DBE lower than 20 are identified possibly because of their relatively low abundance and limited detection range of FT-ICR MS. After thermal treatment for 30 min, N4VOS porphyrins with DBE of 21 and 20 nearly disappear. This indicates that the two types of N4VOS porphyrins can be more easily degraded by processing and may have different structures from N4VOS with higher DBE values. Our previous work proposed that N4VOS with DBE of 21 might be five-ring cyclic thioether linked with porphyrin ring by molecular stimulation.27 Consequently, it is inferred that the reactive N4VOS with DBE of 20 and 21 may contain five-ring cyclic thioether groups rather than benzothiophene. Their reappearance in the late stage could mainly be attributed to hydrogenation intermediates of porphyrins with higher DBE values. N4VOS porphyrins with DBE higher than 21 present a very similar variation of relative abundance versus time as N4VO porphyrins, as presented in the inserted plot in Figure 3b. As suggested by Qian et al.21 and Zhao et al.,18 these types of N4VOS porphyrins can occur through benzothiophene addition from N4VO porphyrins. The similar variation during thermal process could further confirm the above structures of N4VOS porphyrins. Figure 4a and b show the iso-abundant plots of DBE as a function of carbon number for N4VO and N4VOS porphyrins, respectively. The corresponding plots in the high DBE part are enlarged separately on the right. Obviously, the carbon number in the center mass for each type of porphyrins becomes smaller as the reaction time increases. This result agrees well with Figure 2. It is indicated that in addition to hydrogenation, petroporphyrins have also been subjected to extensive thermal cracking reactions, resulting in the formation of vanadyl porphyrins with a shorter size chain attached with the porphyrinic ring. This is consistent with the report of Liu et al.16 The demetallization reaction in our work is much milder than that reported by Liu et al.16 due to the absence of catalysts as well as the low pressure and short time. Therefore, most of the N4VO porphyrins can still be identified here. Overall, during noncatalytic thermal process under hydrogen, petroporphyrins could be demetallized in two possible reaction pathways: thermal cracking reactions, hydrogenation and subsequent rapid hydrogenolysis. 3.3. Transformation of Oxygen and Nitrogen-Containing Vanadyl Porphyrins by Positive-Ion ESI FT-ICR MS. Recently, vanadyl porphyrins with different numbers of additional oxygen and nitrogen atoms have been reported by several researchers.17,18,20,29 In the feed FV, three types of N4VO2 (i.e., DPEP, Rhodo-ETIO, and Rhodo-DPEP) and Rhodo-ETIO N5VO2 porphyrins with low abundance are identified by accurate mass measurement. Figure 5 illustrates iso-abundance plots of DBE as a function of carbon number for these vanadyl porphyrins. It is noteworthy that a considerable proportion of new types of vanadyl porphyrins are identified after thermal treatment for 30 min. The expanded mass spectra at m/z 542−544 in the feed FV and products are shown in Figure 6. From the exact mass measurement and isotope distribution, new types of vanadyl porphyrins can be confirmed. N4VO2 porphyrins with DBE lower than 18 and that higher than 20 both appear in the product after 30 min. Three main

Figure 4. Iso-abundance plots of DBE as a function of carbon number for vanadyl porphyrins in the feed FV and products under different reaction times (380 °C, 5 MPa). (a) N4VO, (b) N4VOS.

Figure 5. Iso-abundance plots of DBE as a function of carbon number for oxygen and/or nitrogen-containing vanadyl porphyrins in the feed FV and products under different reaction times (380 °C, 5 MPa).

types of N4VO3 porphyrins with DBE ranging from 18 to 20 and N5VO2 with DBE ranging from 16 to 20 are also observed. As time increases to 60 min, only N4VO2 with DBE of 21 D


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Figure 6. Expanded mass spectra at m/z 542 and 543 for the feed FV and products under different reaction times (380 °C, 5 MPa).

Figure 7. UV−vis spectra of the feed FV and products from thermal process with or without sulfur under different hydrogen pressures (380 °C).

survive among the emerging vanadyl porphyrins. When the vanadyl porphyrins are thermally reacted for 120 min, only the most abundant types of N4VO2 porphyrins survive from the severe conditions. The same phenomenon is observed for N4VO3 and N5VO2 porphyrins. It can be predicted that, under more severe conditions, the new vanadyl porphyrins would be hydrogenated and demetallized, leaving few that could be detected. It is generally believed that metalloporphyrins tend to be trapped by large molecules, such as asphaltenes.30,31 The FV subfraction presents a high polarity. Interaction between metalloporphyrins and polar molecules could affect the mass spectral identification. Consequently, it can be inferred that the new detected types of petroporphyrins could possibly derive from disassociation of large polar molecules in addition to chemical transformation. Appropriate thermal treatment under mild conditions would greatly facilitate the comprehensive characterization of petroporphyrins by disassociating from large molecules. 3.4. Effect of Atmosphere and Pressure on Transformation of Vanadyl Porphyrins. Petroporphyrins were exposed to complex atmospheres during thermal treatment under hydrogen. The effect of hydrogen sulfide and hydrogen pressure on transformation of vanadyl porphyrins was simultaneously studied. Figure 7 shows the result of UV−vis analysis. By model metalloporphyrins, it is found that both hydrogen sulfide and high hydrogen pressure could promote the hydrogenation conversion.5,6,28 It can be seen from Figure 7 that presence of hydrogen sulfide leads to the decrease of characteristic absorption of vanadyl porphyrins, consistent with results from model compounds. However, hydrogen pressure has little effect on the characteristic absorptions in UV−vis spectrum of petroporphyrins. As above-mentioned, variation of the absorption can only indicate the change of metalloporphyrins apparently. The structural transformation of petroporphyrins was then investigated by ESI FT-ICR MS. Figure 8 shows the DBE distribution of N4VO and N4VOS porphyrins under different conditions. For N4VO porphyrins, an obvious decrease of relative abundance of CnH2n−28N4VO is observed in the thermal products under 20 MPa in the two cases with or without sulfur. As a result, the abundance of N4VO porphyrins with higher DBE all increases with different degrees. For N4VOS porphyrins, the relative abundance for species with DBE lower than 23 increases as pressure rises,

Figure 8. DBE distribution for N4VO and N4VOS porphyrins in products with or without sulfur under different hydrogen pressures (380 °C). (a) N4VO, (b) N4VOS.

indicating their extensive hydrogenation reactions. Considering that N4VO and N4VOS porphyrins have similar structures and present alike structural changes during thermal process, the obvious decrease of CnH2n−28N4VO may arise from the rapid E


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Figure 9. Iso-abundance plots of DBE as a function of carbon number for the feed FV and products with or without sulfur under different hydrogen pressures (380 °C). (a) N4VO, (b) N4VOS, (c) N4VO2.

severe conditions, the new classes (i.e., N5VO2, N4VO3) are no longer found in the product due to their demetallization reactions and low abundance. Figure 9c shows the iso-abundant plot for N4VO2 porphyrins in the products under different conditions. Both high hydrogen pressure and H2S could improve their demetallization reactions. N4VO2 porphyrins with DBE of 17 and 19 are most resistant to thermal treatment. 3.5. Transformation of Nickel Porphyrins by PositiveIon ESI FT-ICR MS. Nickel porphyrins from OSAR and LHAR have been successfully characterized by positive-ion ESI FTICR MS in our previous work.27 Accumulation of nickel porphyrins is very difficult due to the low content of nickel in the feeds. In this study, we attempted to obtain the nickel porphyrins and tentatively studied the transformation by FTICR MS. As previously reported,27 nickel porphyrins are detected as both radical ions and protonated analytes. For convenience of discussion, the relative abundances of these two analytes corresponding to the same types have been combined. Figure 10 shows the DBE distribution for nickel porphyrins based on the mass analysis. Consistent with result from transformation of vanadyl porphyrins, the relative abundance of species with lower DBE increases with the increase of time. It indicates their hydrogenation reactions. Species with DBE of 16

hydrogenolysis of vanadyl porphyrins after hydrogenation. The hydrogenated N4VOS species with DBE lower than 23 could be detected due to its relatively high stability compared to hydrogenated N4VO species. In the presence of sulfur, the relative abundance of classes with low DBE values increases obviously, confirming that hydrogen sulfide could promote the hydrogenation of petroporphyrins. Figure 9a and b shows the iso-abundant plots of DBE versus carbon number for N4VO and N4VOS porphyrins in the products under different conditions, respectively. It is wellknown that hydrogen can inhibit the thermal cracking reactions during thermal process.32 Thus, the carbon number distribution is little affected by increasing hydrogen pressure. Instead, hydrogen pressure plays a significant role in the hydrogenation reactions that can be expressed in the aforementioned DBE distribution. However, when the pressure is up to 20 MPa, a narrower and smaller carbon number is presented, especially for N4VOS porphyrins. This can be ascribed to the hydrodemetallization of petroporphyrins, which agrees well with results from DBE distribution analysis. With the addition of sulfur, the carbon number tends to shift to a slightly lower mass range. It is indicated that hydrogen sulfide could also promote the thermal cracking reactions of petroporphyrins. Under F


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Figure 11. Iso-abundance plots of DBE as a function of carbon number for the feed FNi and products under different reactions times (380 °C, 5 MPa).

ins have been subjected to extensive thermal cracking reactions. Some new species might be formed from dissociation of large molecules, suggesting that appropriate mild thermal treatment may be helpful for more petroporphyrins interacting with catalysts. Finally, nickel porphyrins and the different vanadyl porphyrins species (including N4VO, N4VOS, N4VO2, and N5VO2) present various carbon number distribution and different reactivity. The catalysts with macropore size distribution would be active for all the species removed.

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CONCLUSIONS Structural changes between feed petroporphyrins subfraction and product by ESI FT-ICR MS are studied in order to probe their transformation during noncatalytic thermal process under hydrogen. Three main vanadyl porphyrins (i.e., N4VO, N4VOS and N4VO2) and a fraction of N5VO2 are identified in the feed fraction. Analysis of the variation of DBE and carbon number distribution for N4VO reveals the two possible pathways of thermal demetallization of petroporphyrins, i.e., hydrogenation and rapid hydrogenolysis reactions, and thermal cracking reactions. N4VOS porphyrins show very similar structural transformation with N4VO. A considerable proportion of new types of N4VO2, N4VO3 and N5VO2 are identified by accurate mass measurement and isotopic distribution under mild conditions. It is inferred that the new species could most possibly derive from disassociation of large molecules in addition to chemical transformation. H2S and high hydrogen pressure could promote the hydrogenation of petroporphyrins. H2S can also enhance their thermal cracking while high hydrogen pressure inhibits it. Transformation of nickel porphyrins is consistent with that of vanadyl porphyrins. Analysis of the petroporphyrins at the molecular level reveals their behavior and transformation during thermal process under hydrogen and could also benefit the catalysts design in HDM process.

Figure 10. DBE distribution of the feed FNi and products under different reaction times (380 °C, 5 MPa). (a) OSAR, (b) LHAR.

appear in the product of FNi from OSAR and those with DBE of 19 even disappear in product of FNi from LHAR. When reaction time is 120 min, the relative abundance of species with lower DBE further decreases for OSAR. This may be attributed to the demetallization of metalloporphyrins. However, it is the contrary case for FNi from LHAR. This result might be caused by the different reactivity of these two nickel porphyrins subfractions determined by properties of oil matrixes as well as the structures of nickel porphyrins. Figure 11 shows the iso-abundant plots of DBE versus carbon number for nickel porphyrins in the products from the two feeds. The carbon number in the center mass for each type of porphyrins becomes smaller as time rises, illustrating that petroporphyrins have been subjected to thermal cracking reactions. It agrees well with results for vanadyl porphyrins. Additionally, it seems that vanadyl porphyrins show more extensive cracking reactions than nickel porphyrins. The above analysis of petroporphyrins-concentrated subfractions by ESI FT-ICR MS reveals the behavior and transformation of different vanadyl porphyrins species and nickel porphyrins during noncatalytic thermal process under hydrogen. It could also benefit the catalysts design during HDM. Consistent with reports of Liu et al.,16 the catalysts should have active hydrogenolysis property since petroporphyr-

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Hammami, A., Marshall, A. G., Eds.; Springer: New York, 2005; pp 63−93. (24) Bonné, R. L. C.; van Steenderen, P.; Moulijn, J. A. Appl. Catal., A 2001, 206, 171−181. (25) Rankel, L. A. Degradation of Metalloporphyrins in Heavy Oils Before and During Processing: Effect of Heat, Air, Hydrogen and Hydrogen Sulfide on Petroporphyrin Species. In Metal Complexes In Fossil Fuels: Geochemistry, Characterization, and Processing; Filby, R. H., Branthaver, J. F., Eds.; American Chemical Society: Washington, DC, 1987; pp 257−264. (26) Xu, H.; Que, G.; Yu, D.; Lu, J. R. Energy Fuels 2005, 19, 517− 524. (27) Liu, H.; Mu, J.; Wang, Z.; Ji, S.; Shi, Q.; Guo, A.; Chen, K.; Lu, J. Energy Fuels 2015, 29, 4803−4813. (28) Liu, H.; Ji, S.; Wang, Z.; Guo, A.; Chen, K. Energy Technol. 2015, 3, 145−154. (29) Zhao, X.; Shi, Q.; Gray, M. R.; Xu, C. Sci. Rep. 2014, 4, 5373. (30) Yin, C.-X.; Tan, X.; Müllen, K.; Stryker, J. M.; Gray, M. R. Energy Fuels 2008, 22, 2465−2469. (31) Acevedo, S.; Guzmán, K.; Labrador, H.; Carrier, H.; Bouyssiere, B.; Lobinski, R. Energy Fuels 2012, 26, 4968−4977. (32) Ji, S.; Zhou, Y.; Chen, K.; Wang, Z. Energy Technol. 2015, 2, 877−881.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors thank Professor Quan Shi from China University of Petroleum for the support of FT-ICR MS analysis. This work was supported by the National Natural Science Foundation of China (NSFC) (U1362101), the Fundamental Research Funds for the Central Universities (14CX02120A), the China National Petroleum Corporation (CNPC) Foundation under the Grant “Research and Development for Commercial Application of Novel Technologies in Processing Inferior Heavy Oil” (PRIKY15002, PRIKY15009), the Natural Science Foundation of Shandong Province, China (ZR2014BQ030), and the Application Research of Independent Innovation Foundation of Qingdao (15-9-1-77-jch).

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