Molecular Structure of Heavy Petroleum: Revealed by Molecular

Article Cite This: Energy Fuels XXXX, XXX, XXX−XXX

pubs.acs.org/EF

Molecular Structure of Heavy Petroleum: Revealed by Molecular Composition of Ruthenium-Ion-Catalyzed Oxidation Products Xibin Zhou,†,‡ Suoqi Zhao,† Chunming Xu,† Keng H. Chung,† and Quan Shi*,† †

State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing 102249, China College of Basic Science, JinZhou Medical University, Jinzhou, Liaoning 121001, China

‡

Downloaded by UNIV OF SOUTHERN INDIANA at 04:10:54:530 on June 01, 2019 from https://pubs.acs.org/doi/10.1021/acs.energyfuels.9b00341.

S Supporting Information *

ABSTRACT: Ruthenium-ion-catalyzed oxidation (RICO) is an approach for investigating the structure of heavy oils by selectively removing aromatic carbon from petroleum fractions, while leaving the structural integrity of aliphatic units intact. Six petroleum vacuum residue (VR) samples originating from various sources were separated into saturate, aromatic, resin, and asphaltene (SARA) fractions. The aromatics, resins, and asphaltenes were subjected to the RICO reaction, and the products were characterized by gas chromatography (GC) and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The alkyl side chains on aromatic cores of various VRs were significantly different in terms of their contents and carbon number distribution ranges. Normal alkyl side chains were dominant in all VRs; isoparaffin side chains were ubiquitous but in low concentrations, even in severely biodegraded oils. The content of the methyl group was much more than those of other alkyl groups and the content of the side chain decreased with an increased carbon number. For a given VR, the aromatics, resins, and asphaltenes had similar alkyl side chains, especially for aromatics and resins. The archipelago structures were rare, if they existed; nevertheless, asphaltenes appeared to have relatively more archipelago structures than aromatics and resins. FT-ICR MS analysis indicated that many structural moieties, except alkyl side chains, were connected to aromatic cores, which were abundant. The upper limits of the carbon number of alkyl chains determined by FT-ICR MS analysis were much higher than those obtained by GC analysis. For a given VR, the upper limits of the side chain carbon number in aromatics, resins, and asphaltenes were comparable. The relative abundances of short chains and naphthenic structures in asphaltenes were higher than those in resins and aromatics.

1. INTRODUCTION Physicochemical properties and reactions of heavy oils are strongly correlated with their chemical compositions and molecular structures, which are dependent on oil types from various geological origins and/or processing techniques.1 A better understanding of molecular composition and structure of heavy oil is needed to optimize the petroleum process. Many techniques have been used to characterize the molecular composition and/or structure of heavy fractions of fossil fuels, such as elemental analysis, nuclear magnetic resonance,2−4 X-ray absorption near-edge structure,5 X-ray diffraction,2 vapor pressure osmometry,6 and Fourier transform infrared spectrometry.7,8 Microscopy techniques, such as highresolution transmission electron microscopy9 and low-temperature atomic force microscopy,10 can be used to analyze a single molecule. The high-resolution mass spectrometry coupled with various soft-ionization techniques have been used to characterize the molecular composition of heavy oil, which revealed the chemical diversity of the super-complex mixtures.11−23 Ionization is a prerequisite for mass spectrometry analysis. In conjunction with various complementary technologies, chemical derivatization techniques were developed to allow selective and precise analysis of specific compounds. For example, sulfur compounds in petroleum can be analyzed by oxidation− reduction,24,25 methylation,19 and demethylation for sulfur compound speciation.26,27 The derivatization method for large molecular saturates analysis by using ruthenium-ion-catalyzed © XXXX American Chemical Society

oxidation (RICO) followed by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS).28,29 Using this method, saturates were oxidized into alcohols, which enabled ionization in negative-ion electrospray ionization (ESI). Large molecular carboxylic acids, in conjunction with other heteroatoms, can be analyzed by ESI FT-ICR MS. Combined with gas chromatography (GC), a semiquantitative analysis of normal, isomeric, and naphthenic hydrocarbons was determined.29 Initially, the RICO method alone was widely used for molecular structure characterizing of fossil fuels.30−44 RICO can selectively transform the aromatic structure of heavy oil molecules, and preserve the aliphatic structure by transforming into the corresponding carboxylic acid.45 The composition of RICO products obtained by GC analysis can provide structural information of aromatic cores and their substitute aliphatic side chains. However, the GC analysis is limited to small molecules. In this work, six petroleum vacuum residue (VR) samples were separated into saturate, aromatic, resin, and asphaltene (SARA) fractions and subjected them to RICO reactions. The reaction products were characterized by GC and FT-ICR MS. The molecular structures of VR-derived SARA fractions were discussed. Received: February 1, 2019 Revised: April 26, 2019

A

DOI: 10.1021/acs.energyfuels.9b00341 Energy Fuels XXXX, XXX, XXX−XXX

Article

Energy & Fuels

in a previous study.46 Each VR-derived subfraction (0.3 g) was dissolved in 20 mL of CCl4 in a 100 mL flask, followed by adding the following reagents in sequence: 20 mL of CH3CN, 20 mL of water, 5 g of NaIO4, and 20 mg of RuCl3. A short condenser was connected to the flask, which was heated on a 40 °C heating plate. The mixture in the flask was continuously stirred with a magnetic bar. During the experiment, a continuous flow of nitrogen gas was used to purge the product CO2 through a column packed with calcium chloride (CaCl2) particles to adsorb moisture. The product gas was fed to another column packed with 20 mesh granular sodium hydroxide (NaOH), CaCl2, and metal sodium particles. Safety precautions should be exercised in performing the experiment using a highly reactive metal. The yield of CO2 was determined from the weight increase of the column. The color of the reaction mixture changed slowly from black to pale during the reactions. The experiment was terminated after 24 h. The reaction product was an emulsified suspension mixture, consisting of an organic phase, aqueous phase, and tiny particles of NaIO3. The product mixture was separated by filtration using a quantitative filter paper. The precipitate collected on the filter paper was washed with 10 mL of CH2Cl2. The aqueous and organic phases were separated by a separating funnel. The aqueous phase was extracted with 10 mL of CH2Cl2 two times. The organic phase and the CH2Cl2 solution were combined. After desiccation with anhydrous Na2SO4, the liquid was transferred into a 100 mL volumetric flask and cooled to room temperature. One hundred microliters of CCl4 solution of n-docosane (2 mg/mL) was added to the mixture as the internal standard for quantitative analysis of largemolecular-weight alkyl carboxylic acids. The total volume of the organic phase was determined to be 100 mL with CH2Cl2, and then 1 mL of the solution was taken out from the flask for analysis by ESI FT-ICR MS, GC, and GC−MS. The rest of the solution in the flask was dried using a rotary evaporator and methylation with CH2N2. The product methyl esters of acids were subjected to GC and GC−MS analyses. The aqueous phase was transferred into a 25 mL volumetric flask and the volume was determined at 25 mL with water. One milliliter of the solution was taken out from the flask for ESI FT-ICR MS, GC, and GC−MS analyses. The rest of the solution in the flask was dried using a rotary evaporator. The carboxylic acids were extracted by acetone, followed by methylation with CH2N2. The product methyl esters of acids were subjected to GC and GC−MS analyses. 2.3. Analyses. A Thermo-Finnigan Trace 2000 GC coupled with a DSQ mass detector and an Agilent 7890A GC coupled with a flame ionization detector, were used to characterize the RICO reaction products. The mass spectrometer was equipped with an EI source at 70 eV ionization energy and set to a scan range of 35−500 Da in a 1 s period. The low-molecular-weight carboxylic acids were directly

2. EXPERIMENTAL SECTION 2.1. Materials. Six VR samples were obtained from various heavy oils: Liaohe, Tahe, and Dagang from China, Venezuela Orinoco heavy oil, Canada Athabasca bitumen, and Sudan heavy oil. The Liaohe VR was obtained from a commercial vacuum distillation unit operated at 420 °C cut-point, at the PetroChina Liaohe Petrochemical Company. Other VR samples were 500 °C+ residue obtained from a laboratory vacuum distillation unit.46 The fractionation of each VR sample into SARA was carried out according the Chinese Standard Analytical Method for Petroleum and Natural Gas Industry: SH/T 0509-92 (equivalent to ASTM D2007-93). 2.2. Ruthenium-Ion-Catalyzed Oxidation. The RICO reactions of VR-derived subfractions and analyses of reaction products are shown in Figure 1. The analyses of saturates’ fractions were reported

Figure 1. Experimental scheme and characterization.

Table 1. Elemental Analysis of VR and Subfractions Liaohe % C H S N H/C

% C H S N H/C

Venezuela

Canada

total

Sat

Aro

Res

Asp

total

Sat

Aro

Res

Asp

total

Sat

Aro

Res

Asp

88.40 10.93 0.47 0.98 1.48

18.06 84.57 13.95 0.27 0.01 1.97

24.28 86.89 11.45 0.52 0.09 1.57 Tahe

37.45 85.41 9.89 0.47 1.49 1.38

20.20 83.82 7.45 0.40 1.92 1.06

82.69 9.68 4.80 0.98 1.40

7.30 84.34 14.21 0.21 0.03 2.01

32.36 81.92 11.23 4.09 0.03 1.63 Dagang

37.23 80.59 9.83 4.68 1.09 1.45

14.58 80.26 7.86 5.35 1.46 1.17

82.97 9.65 6.00 0.67 1.39

8.27 84.30 14.27 0.43 0.01 2.02

41.06 80.99 10.79 5.45 0.01 1.59 Sudan

36.22 79.33 9.61 5.94 0.74 1.44

14.46 74.57 7.30 7.64 0.79 1.17

total

Sat

Aro

Res

Asp

total

Sat

Aro

Res

Asp

32.82 85.18 12.10 0.20 0.20 1.69

42.04 84.48 10.69 0.27 1.01 1.51

0.00 86.64 11.64 0.17 0.65 1.60

17.50 83.35 14.86 0.01 0.01 2.12

40.78 84.64 11.87 0.09 0.36 1.67

41.73 83.82 10.95 0.19 0.93 1.56

0.00

87.43 11.68 0.24 0.70 1.59

25.14 84.12 14.85 0.32 0.01 2.10

total

Sat

Aro

Res

Asp

82.21 9.50 2.97 0.53 1.38

13.56 84.16 14.63 0.30 0.03 2.07

33.91 83.69 10.55 3.14 0.02 1.50

22.66 83.09 9.03 3.16 0.94 1.30

29.87 78.99 6.34 3.84 1.05 0.96

B


Article

Energy & Fuels

Figure 2. Broadband negative-ion ESI FT-ICR mass spectra of various VRs and relative abundances of various class species assigned from the mass spectra. Different colors corresponding to compounds’ series with various DBEs.

Figure 3. GC−MS total ion chromatograms of acid methyl esters in the organic phase of RICO reaction products. N-docosane was co-injected as the internal standard. analyzed by using a HP-FFAP capillary GC column (30 m × 0.25 mm × 0.25 μm) (Agilent Ltd.). The methyl esters of high-molecularweight alkyl carboxylic acids were analyzed by a HP-5MS (30 m × 0.25 mm × 0.25 μm) fused silica capillary column (Agilent Ltd.). A Bruker apex-ultra FT-ICR MS equipped with a 9.4 T superconducting magnet was used for the molecular characterization of the RICO reaction products. An ESI source was used and operated in negative-ion mode. The ESI FT-ICR MS operating conditions, mass calibration, and data analysis are described in the Supporting Information.

were substantial. The high sulfur contents of Venezuela, Canada, and Tahe VRs were at 4.80, 6.00, and 2.97 wt %, respectively. Tahe VR had the lowest H/C ratio and the highest asphaltene content, and its asphaltenes had the lowest H/C ratio among all VRs and their asphaltene fractions. Sulfur and nitrogen contents of SARA fractions increased gradually from saturates to asphaltenes, indicating the enrichment of heteroatoms in the polar components. Figure 2 shows the negative-ion ESI FT-ICR MS broadband (m/z 200−1200) spectra and relative abundances of various heteroatom class species for various VRs. The abundant heteroatom class species include N1−2, N1−2O1−3, N1S1−2, O1−5, N1O1−2, S1, and O1−2S1−2. The spectra of Tahe, Venezuela, and Canada VRs showed relatively high abundance of NxSy and/or

3. RESULTS AND DISCUSSION 3.1. Bulk Properties and Molecular Compositions of VR. Table 1 shows the elemental analyses of various VRs and their SARA subfractions. Dagang and Sudan VRs had negligible amounts of asphaltenes, whereas other four VRs C


Article

Energy & Fuels

Figure 4. (a) Contents of normal (n-) alkyl monocarboxylic acids (red area) and n-dicarbonxylic acids (gray area) in RICO reaction products of VR fractions (aromatics, resins, and asphaltenes). (b) Ion-relative abundance distribution of DBE vs carbon number for O2 class species assigned from negative-ion ESI FT-ICR mass spectra of RICO reaction products.

Tahe VRs were petroleum-derived from marine formations, which have the characteristics of high sulfur-containing species. The Venezuela, Canada, Tahe, and Liaohe VRs were severely biodegraded in petroleum formations, leading to low H/C

OxSy compounds, which were consistent with high heteroatoms in these VRs. The different compositions among the VRs can be attributed to different geological origins. The Venezuela, Canada, and D


Article

Energy & Fuels

Figure 5. Broadband negative-ion ESI FT-ICR mass spectra of RICO reaction products of various VRs. The stearoc-d35 acid was co-injected as the internal standard.

phase and the aqueous phase of RICO reaction products are shown in Figures S1−S4 (see the Supporting Information). The compositions of n-aliphatic monocarboxylic acids and ndicarbonxylic acids determined by GC and GC−MS analyses are plotted in Figure 4a. Figure 4b shows the relative-ion abundance distribution of the double-bond equivalent (DBE) as a function of carbon number of O2 class species determined by FT-ICR mass spectra (shown in Figure 5). The O2 class species with 1 DBE and 2−6 DBE are likely alkanoic acids and naphthenic acids, respectively, which are paraffinic and naphthenic groups attached to the aromatic core by the C− C bond with alkyl chains and 1−5 naphthenic rings. According to RICO reaction mechanisms, the monocarboxylic acids were derived from alkyl chains on the aromatic cores, and ωalkanoic diacids were derived from bridge linkages between aromatic cores. The origin of monocarboxylic acids is widely accepted in the field; however, the ω-alkanoic diacids may not necessarily derive from bridge linkages between aromatic cores. Compositional information in Figures 3 and 4 can be summarized as follows:

ratios and high asphaltene contents, which exhibited low molecular weights in their mass spectra. Biodegradation is known to preferentially deplete normal alkyl chains of petroleum molecules, resulting in enrichment of condensed core structures with short side chains. The Tahe oil was different from other biodegraded oils, which were buried deeply and matured after a severe biodegradation process. As a result, naphthenic acids, which are abundant in biodegraded oils, were decomposed in Tahe oil. 3.2. Compositional Characterization of RICO Reaction Products by GC and GC−MS. The acid compounds in RICO reaction products in organic-soluble and water-soluble portions were analyzed by GC and GC−MS, respectively. The RICO reaction products were injected directly into GC and GC−MS to analyze the small-molecular-weight acids. The large-molecular-weight acids were converted into corresponding methyl esters and analyzed by GC and GC−MS. Figure 3 shows the GC−MS chromatograms of acid methyl esters in the organic phase of RICO reaction products from aromatics, resins, and asphaltenes of various VRs. Gas chromatograms of low-molecular-weight acids- and highmolecular-weight acids-derived methyl esters of the organic

(1) The composition of monocarboxylic acids varied significantly among VRs in terms of the content and E


Article

Energy & Fuels

Figure 6. Relative abundance of class species assigned from negative-ion mass spectra of RICO reaction products (organic phase) from various VRs.

(5) The concentration of ω-alkanoic diacids was 2 orders of magnitude lower than that of monocarboxylic acids and the length of alkyl chains was much shorter than that of monocarboxylic acids. Even if the ω-alkanoic diacids were derived from bridge linkages, the number of these moities were very low. In other words, the archipelago structures were rare, if they existed. Asphaltenes had a relative higher concentration of ω-alkanoic diacids than aromatics and resins (except Tahe VR), but the difference was small. The anomaly (asphaltenes with low concentration of ω-alkanoic diacids) of Tahe VR suggests that the ω-alkanoic diacids are more relevant to native acids in the oil, as the acids in Tahe oil decomposed under high reservoir temperature.

distribution range. As shown in Figure 3, the acids in Canada, Venezuela, and Tahe VRs exhibited the distribution range of carbon number of C2−C20 (based on 0.1 mmol/100 g oil concentration, as shown in Figure 4) and the relative abundance decreased drastically with increased carbon number. The upper limits of carbon number of acids in other VRs were higher than C30 and their relative abundance was constant over a wide range. The composition was dependent on the degree of biodegradation, which was consistent with H/C ratios of various VRs, as shown in Table 1. The Liaohe oil was a highly biodegraded conventional crude oil, exhibiting average composition values among the oils considered in this study. The total number of side chains of aromatic compounds in various VRs were similar. Therefore, the degree of biodegradation should be the dominant factor to determine the distribution of carbon number. (2) For a given VR, the aromatics, resins, and asphaltenes had similar composition of monocarboxylic acids, especially aromatics and resins. There were only small concentration differences in some VRs, such as Liaohe and Tahe (see Figure S5 in the Supporting Information). (3) The number of methyl groups (corresponding to C2 acid) was much more than other alkyl groups. As the logarithmic coordinates were used in Figure 4, the concentration difference between methyl and ethyl groups (corresponding to C2 and C3, respectively) was 10 times. In general, the number of alkyls decreased with increased carbon number. The VRs with a lesser degree of biodegradation exhibited a constant relative abundance in mid carbon number ranges. (4) Normal alkyl side chains (acids) were dominant in all VRs. Isopariffin side chains (iso-alkanoic acids) were detected in all samples, but the relative abundance was much lesser than normal alkyl moieties, even in the severely biodegraded VRs.

3.3. FT-ICR MS Analysis. Figure 5 shows the broadband negative ESI FT-ICR mass spectra of organic-soluble RICO reaction products derived from various VRs. The spectrum peak marked with a red arrow was the internal standard (stearic-d35 acid, m/z 318.4839) which can be used to compare the relative abundances among various VRs. The mass ranges of the Liaohe, Venezuela, Canada, and Tahe VRs were 200− 650, whereas Dagang and Sudan exhibited a wider mass range of 200−750. The results were consistent with those of GC− MS analysis, although the FT-ICR MS analysis covered a wider range of carbon number. To compare the small differences among aromatics, resins, and asphaltenes, the mass peaks were divided into four ranges: 550. The sum of mass peak relative abundances for each mass range was calculated and summarized in Figure S6 (see the Supporting Information). The relative abundance of low mass range peaks in asphaltenes was higher than resins, and aromatics, whereas that of high mass range peaks exhibited an opposite trend in which the aromatics were the most abundant. As shown in Figure 5, the contents of carboxylic acids in RICO reaction products from various VRs and their fractions were distinctly different by comparing the relative abundance of the internal standard. F


Article

Energy & Fuels

Figure 7. Semiquantitative result of total and cyclic monocarboxylic acids at the whole mass range by a combination of FT-ICR MS and GC results.

Figure 6 shows the relative abundance of class species from resin RICO reaction products of various VRs. The Ox (x = 2− 12), SOx (x = 4−12), and NOx (x = 3−11) class species were detected. The composition of RICO reaction products was much more complex than that obtained by traditional methods, such as GC. The results suggest that many structural moities other than alkyl side chains could be connected to the aromatic cores. As ESI FT-ICR MS is capable of detecting

nonvolatile compounds, it is a complementary technique for characterizing RICO reaction products. However, it should be noted that the composition shown in Figure 6 was not just an expansion in detection range. The FT-ICR MS has a severe discrimination in the low mass range, which is an inherent instrumental issue resulting in underestimating of lowmolecular-weight carboxylic acids (low DBE O2 class species). In other words, the true abundance of the O2 class species G


Article

Energy & Fuels

Figure 8. Ion-relative abundance distribution of DBE vs carbon number for SO4 class species assigned from the negative-ion ESI FT-ICR mass spectra of the RICO products. The speculated structures illustrate a possible pathway of the RICO reaction.

of side chains in aromatics, resins, and asphaltenes were similar. In our previous study,29 a semi-quantitative method was developed for analyzing of O2 class species in RICO reaction products. In this work, the same method was used to analyze VR subfractions and the results are shown in Figure 7. The O2 species with 1 DBE are likely alkanoic acids, which were n- and iso-alkyl groups attached to aromatic core by a single C−C bond. Compounds with 2−6 DBE were 1−5 ring naphthenic moities. The results show that the dominant nonaromatic moiety connected to aromatic cores were alkanes, followed by a very small proportion of naphthenics. 3.4. Sulfur and Nitrogen Compounds in RICO Reaction Products. As shown in Figure 6, the lowest xvalue of SOx class species for fractions in the Venezuela, Canadian, and Tahe VRs was 4, suggesting that SOx class species could be a combination of sulfone (SO2) and

should be much more than that shown in Figure 6, as indicated by the results of GC analysis. As shown in Figure 4b, the relative-ion abundance distribution of DBE as a function of carbon number of O2 class species indicates that naphthenic structures with 1−5 rings were abundant in various VRs. A summary of relative abundances of carboxylic acids with various rings in aromatics, resins, and asphaltenes are shown in Figure S7 (see the Supporting Information). The ratio of naphthenic structures in aromatics was higher than that in resins and asphaltenes, as aromatics have a low degree of molecular condensation. The upper limit of carbon number range of O2 class species was 50 as shown in Figure 4b. By optimizing the operating condition of FT-CIR MS for high mass ranges, the upper limit of carbon number of the Sudan VR was 75 (as shown in Figure S8 in the Supporting Information), which is far exceeding the detection limit of GC. For a given VR, the upper limits of carbon number H


Article

Energy & Fuels

Figure 9. Ion-relative abundance distribution of DBE vs carbon number for NO3 class species assigned from the negative-ion ESI FT-ICR mass spectra of the RICO products. The speculated structures illustrate a possible pathway of the RICO reaction.

carboxylic groups (On), which is consistent with the previous study. The sulfone structure was an oxidation product from the RICO reactions, instead of naturally occurring, as it was also presented in the aromatic fraction. Figure 8 shows the relativeion abundance plots of DBE as a function of carbon number

for the SO4 class species in the organic phase. For all the samples, the 1 DBE series was absent, indicating that the types of sulfide in VR molecules were cyclic sulfide groups. Figure 9 also shows that the relative abundance of SO4 with more than two rings in aromatic fractions was significantly more than that I


Article

Energy & Fuels of resins and asphaltenes, which was consistent with the above findings in which the ratio of the naphthenic structure in the aromatics was higher than that in resins and asphaltenes. The lowest oxygen atom number of NOx class species was 3, suggesting that NO3 could be a combination of NO and carboxylic groups (O2). Figure 8 shows the relative-ion abundance plots of DBE as a function of carbon number for the NO3 class species in the organic phase. Similar to the SO4 compounds, the 1 DBE series was absent for all samples. The possible precursor of NO3 and the reaction pathway of the RICO reactions are shown in Figure 9. The results indicate that the amine structures in VR molecules were predominantly cyclic secondary or tertiary amines. 3.5. Carbon Recovery. Carbon recovery is an important parameter to evaluate the RICO reaction experiments. The percentage of equivalent carbon in asphaltenes for monoacid, di-n-alkanoic acid, benzene carboxylic acids, CO2, and the total carbon recovery were calculated and are listed in Table S1 (see the Supporting Information). The carbon recovery varied from 18.7 to 42.7%. Methyl and carbon dioxide were the main contributors to carbon recovery. The carbon recovery of Dagang and Sudan VRs were unexpectedly low because of a relative low content of the methyl group and high H/C ratio (low aromatic carbon content). The carbon recovery increased in the order of aromatics, resins, and asphaltenes. The low carbon recovery indicated that the observed RICO reaction products accounted for one piece of a jigsaw. The unrecovered portion should include the di-iso-alkanoic acid, diacid naphthenic derivatives, the oxidation products of O2 and O4 species, SOx and NOx compounds.

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Phone: +86 10 89739157. ORCID

Suoqi Zhao: 0000-0003-3707-2844 Quan Shi: 0000-0002-1363-1237 Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS The authors thank Yahe Zhang and Peidong Wang for assisting with the GC and FT-ICR MS analysis. This work was supported by the National Natural Science Foundation of China (NSFC 41773038).

■

REFERENCES

(1) Mullins, O. C.; Sheu, E. Y.; Hammami, A.; Marshall, A. G. A. Heavy Oils and Petroleomics; Springer: New York, 2007. (2) Trejo, F.; Ancheyta, J.; Morgan, T. J.; Herod, A. A.; Kandiyoti, R. Characterization of Asphaltenes from Hydrotreated Products by Sec, Ldms, Maldi, Nmr, and Xrd. Energy Fuels 2007, 21, 2121−2128. (3) Kelemen, S. R.; Afeworki, M.; Gorbaty, M. L.; Cohen, A. D. Characterization of Organically Bound Oxygen Forms in Lignites, Peats, and Pyrolyzed Peats by X-Ray Photoelectron Spectroscopy (Xps) and Solid-State 13c Nmr Methods. Energy Fuels 2002, 16, 1450−1462. (4) Tsai, P.-J.; Shieh, H.-Y.; Lee, W.-J.; Lai, S.-O. Characterization of Pahs in the Atmosphere of Carbon Black Manufacturing Workplaces. J. Hazard. Mater. 2002, 91, 25−42. (5) Wiltfong, R.; Mitra-Kirtley, S.; Mullins, O. C.; Andrews, B.; Fujisawa, G.; Larsen, J. W. Sulfur Speciation in Different Kerogens by Xanes Spectroscopy. Energy Fuels 2005, 19, 1971−1976. (6) Zhang, L.; Shi, Q.; Zhao, C.; Zhang, N.; Chung, K. H.; Xu, C.; Zhao, S. Hindered Stepwise Aggregation Model for Molecular Weight Determination of Heavy Petroleum Fractions by Vapor Pressure Osmometry (Vpo). Energy Fuels 2013, 27, 1331−1336. (7) Liu, F.-J.; Wei, X.-Y.; Zhu, Y.; Gui, J.; Wang, Y.-G.; Fan, X.; Zhao, Y.-P.; Zong, Z.-M.; Zhao, W. Investigation on Structural Features of Shengli Lignite through Oxidation under Mild Conditions. Fuel 2013, 109, 316−324. (8) Wang, S.; Tang, Y.; Schobert, H. H.; Guo, Y. N.; Su, Y. FTIR and13C NMR Investigation of Coal Component of Late Permian Coals from Southern China. Energy Fuels 2011, 25, 5672−5677. (9) Sharma, A.; Groenzin, H.; Tomita, A.; Mullins, O. C. Probing Order in Asphaltenes and Aromatic Ring Systems by Hrtem. Energy Fuels 2002, 16, 490−496. (10) Schuler, B.; Meyer, G.; Peña, D.; Mullins, O. C.; Gross, L. Unraveling the Molecular Structures of Asphaltenes by Atomic Force Microscopy. J. Am. Chem. Soc. 2015, 137, 9870−9876. (11) Marshall, A. G.; Hendrickson, C. L.; Jackson, G. S. Fourier Transform Ion Cyclotron Resonance Mass Spectrometry: A Primer. Mass Spectrom. Rev. 1998, 17, 1−35.

4. CONCLUSIONS The composition of alkyl side chains on aromatic cores varied significantly among various VRs in terms of their contents and carbon number distribution ranges. Normal alkyl side chains were dominant in all VRs; isopariffin side chains were ubiquitous but in low concentrations, even in severe biodegraded oils. The content of the methyl group was much more than those of other alkyl groups and the content of the side chain decreased with increased carbon number. For a given VR, the aromatics, resins, and asphaltenes had similar alkyl side chains, especially for aromatics and resins. The archipelago structures were rare, if they existed; nevertheless asphaltenes appeared to have relatively more archipelago structures than aromatics and resins. FT-ICR MS analysis indicated that many structural moities, except alkyl side chains, were connected to aromatic cores, which were abundant. The upper limits of carbon number of alkyl chains determined by FT-ICR MS analysis were much higher than those obtained by GC analysis. For a given VR, the upper limits of the side chain carbon number in aromatics, resins, and asphaltenes were comparable. The relative abundances of short chains and naphthenic structures in asphaltenes were higher than those in resins and aromatics.

■

small alkanoic acids in the organic phase and the water phase; gas chromatogram of acid methyl esters in the organic phase and the water phase of RICO reaction product; contents of n-alkyl monocarboxylic acids and dicarbonxylic acids; molecular reaction of RICO reaction products of subfractions of various VRs; relative abundance of various cyclic alkyls of subfractions of various VRs; upper limit of carbon number for alkyl groups of various VRs; and carbon recovery contribution of major RICO reaction products of subreactions of various VRs (PDF)

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.energyfuels.9b00341. GC and GC−MS analysis; ESI FT-ICR MS analysis; mass calibration and data analysis; gas chromatogram of J


Article

Energy & Fuels (12) Hughey, C. A.; Rodgers, R. P.; Marshall, A. G. Resolution of 11 000 Compositionally Distinct Components in a Single Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrum of Crude Oil. Anal. Chem. 2002, 74, 4145−4149. (13) Marshall, A. G.; Rodgers, R. P. Petroleomics: The Next Grand Challenge for Chemical Analysis. Acc. Chem. Res. 2004, 37, 53−59. (14) Rodgers, R. P.; Schaub, T. M.; Marshall, A. G. Petroleomics: MS Returns to Its Roots. Anal. Chem. 2005, 77, 20A−27A. (15) Schaub, T. M.; Hendrickson, C. L.; Quinn, J. P.; Rodgers, R. P.; Marshall, A. G. Instrumentation and Method for Ultrahigh Resolution Field Desorption Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry of Nonpolar Species. Anal. Chem. 2005, 77, 1317−1324. (16) Purcell, J. M.; Hendrickson, C. L.; Rodgers, R. P.; Marshall, A. G. Atmospheric Pressure Photoionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry for Complex Mixture Analysis. Anal. Chem. 2006, 78, 5906−5912. (17) Stanford, L. A.; Kim, S.; Klein, G. C.; Smith, D. F.; Rodgers, R. P.; Marshall, A. G. Identification of Water-Soluble Heavy Crude Oil Organic-Acids, Bases, and Neutrals by Electrospray Ionization and Field Desorption Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry. Environ. Sci. Technol. 2007, 41, 2696−2702. (18) Marshall, A. G.; Rodgers, R. P. Petroleomics: Chemistry of the underworld. Proc. Natl. Acad. Sci. U.S.A. 2008, 105, 18090−18095. (19) Panda, S. K.; Andersson, J. T.; Schrader, W. Characterization of Supercomplex Crude Oil Mixtures: What Is Really in There? Angew. Chem. 2009, 121, 1820−1823. (20) Alshareef, A. H.; Tan, X.; Diner, C.; Zhao, J.; Scherer, A.; Azyat, K.; Stryker, J. M.; Tykwinski, R. R.; Gray, M. R. Binary Interactions in Coke Formation from Model Compounds and Asphaltenes. Energy Fuels 2013, 28, 1692. (21) Headley, J. V.; Peru, K. M.; Mohamed, M. H.; Wilson, L.; Mcmartin, D. W.; Mapolelo, M. M.; Lobodin, V. V.; Rodgers, R. P.; Marshall, A. G. Atmospheric Pressure Photoionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry Characterization of Tunable Carbohydrate-Based Materials for Sorption of Oil Sands Naphthenic Acids. Energy Fuels 2013, 28, 1611. (22) Shi, Q.; Hou, D.; Chung, K. H.; Xu, C.; Zhao, S.; Zhang, Y. Characterization of Heteroatom Compounds in a Crude Oil and Its Saturates, Aromatics, Resins, and Asphaltenes (Sara) and Non-Basic Nitrogen Fractions Analyzed by Negative-Ion Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry. Energy Fuels 2010, 24, 2545−2553. (23) Shi, Q.; Zhao, S.; Xu, Z.; Chung, K. H.; Zhang, Y.; Xu, C. Distribution of Acids and Neutral Nitrogen Compounds in a Chinese Crude Oil and Its Fractions: Characterized by Negative-Ion Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry. Energy Fuels 2010, 24, 4005−4011. (24) Liu, P.; Shi, Q.; Chung, K. H.; Zhang, Y.; Pan, N.; Zhao, S.; Xu, C. Molecular Characterization of Sulfur Compounds in Venezuela Crude Oil and Its Sara Fractions by Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry. Energy Fuels 2010, 24, 5089−5096. (25) Liu, P.; Xu, C.; Shi, Q.; Pan, N.; Zhang, Y.; Zhao, S.; Chung, K. H. Characterization of Sulfide Compounds in Petroleum: Selective Oxidation Followed by Positive-Ion Electrospray Fourier Transform Ion Cyclotron Resonance Mass Spectrometry. Anal. Chem. 2010, 82, 6601−6606. (26) Wang, M.; Zhao, S.; Chung, K. H.; Xu, C.; Shi, Q. Approach for Selective Separation of Thiophenic and Sulfidic Sulfur Compounds from Petroleum by Methylation/Demethylation. Anal. Chem. 2015, 87, 1083−1088. (27) Wang, M.; Zhu, G.; Ren, L.; Liu, X.; Zhao, S.; Shi, Q. Separation and Characterization of Sulfur Compounds in Ultra-Deep Formation Crude Oils from Tarim Basin. Energy Fuels 2015, 29, 4842−4849.

(28) Wang, Y.-G.; Wei, X.-Y.; Xie, R.-L.; Liu, F.-J.; Li, P.; Zong, Z.M. Structural Characterization of Typical Organic Species in Jincheng No. 15 Anthracite. Energy Fuels 2015, 29, 595−601. (29) Zhou, X.; Zhao, S.; Shi, Q. Quantitative Molecular Characterization of Petroleum Asphaltenes Derived Ruthenium Ion Catalyzed Oxidation Product by ESI FT-ICR MS. Energy Fuels 2016, 30, 3758− 3767. (30) Djerassi, C.; Engle, R. R. Oxidations with Ruthenium Tetroxide. J. Am. Chem. Soc. 1953, 75, 3838−3840. (31) Carlsen, P. H. J.; Katsuki, T.; Martin, V. S.; Sharpless, K. B. A Greatly Improved Procedure for Ruthenium Tetroxide Catalyzed Oxidations of Organic Compounds. J. Org. Chem. 1981, 46, 3936− 3938. (32) Stock, L. M.; Tse, K.-T. Ruthenium Tetroxide Catalysed Oxidation of Illinois No.6 Coal and Some Representative Hydrocarbons. Fuel 1983, 62, 974−976. (33) Mojelsky, T. W.; Montgomery, D. S.; Strausz, O. P. Ruthenium (Viii) Catalyzed Oxidation of High Molecular Weight Components of Athabasca Oil Sand Btumen. AOSTRA J. Res. 1985, 2, 131−137. (34) Strausz, O. P.; Mojelsky, T. W.; Lown, E. M. The Molecular Structure of Asphaltene: An Unfolding Story. Fuel 1992, 71, 1355− 1363. (35) Artok, L.; Murata, S.; Nomura, M.; Satoh, T. Reexamination of the Rico Method. Energy Fuels 1998, 12, 391−398. (36) Murata, S.; Tani, Y.; Hiro, M.; Kidena, K.; Artok, L.; Nomura, M.; Miyake, M. Structural Analysis of Coal through Rico Reaction: Detailed Analysis of Heavy Fractions. Fuel 2001, 80, 2099−2109. (37) Strausz, O. P.; Peng, P. A.; Murgich, J. About the Colloidal Nature of Asphaltenes and the Mw of Covalent Monomeric Units. Energy Fuels 2002, 16, 809−822. (38) Wang, Y.-G.; Wei, X.-Y.; Yan, H.-L.; Shi, D.-L.; Liu, F.-J.; Li, P.; Fan, X.; Zhao, Y.-P.; Zong, Z.-M. Structural Features of Extraction Residues from Supercritical Methanolysis of Two Chinese Lignites. Energy Fuels 2013, 27, 4632−4638. (39) Lv, J.-H.; Wei, X.-Y.; Qing, Y.; Wang, Y.-H.; Wen, Z.; Zhu, Y.; Wang, Y.-G.; Zong, Z.-M. Insight into the Structural Features of Macromolecular Aromatic Species in Huolinguole Lignite through Ruthenium Ion-Catalyzed Oxidation. Fuel 2014, 128, 231−239. (40) Nowicka, E.; Sankar, M.; Jenkins, R. L.; Knight, D. W.; Willock, D. J.; Hutchings, G. J.; Francisco, M.; Taylor, S. H. Selective Oxidation of Alkyl-Substituted Polyaromatics Using Ruthenium-IonCatalyzed Oxidation. Chem.Eur. J. 2015, 21, 4285−4293. (41) Shoair, A. G. F. Ultrasonic-Assisted Ruthenium-Catalyzed Oxidation of Some Organic Compounds in Aqueous Medium. J. Mol. Liq. 2015, 206, 68−74. (42) Wang, Y.-G.; Wei, X.-Y.; Xie, R.-L.; Liu, F.-J.; Li, P.; Zong, Z.M. Structural Characterization of Typical Organic Species in Jincheng No. 15 Anthracite. Energy Fuels 2015, 29, 595−601. (43) Wang, S.-K.; Wei, X.-Y.; Liao, Y.-Y.; Wang, Y.-G.; Li, Z.-K.; Xu, D.-D.; Zong, Z.-M. Insight into Structural Feature of the Extraction Residue from Shenmu Coal Char. Fuel Process. Technol. 2016, 150, 23−29. (44) Svalova, A.; Parker, N. G.; Povey, M. J. W.; Abbott, G. D. Determination of Asphaltene Critical Nanoaggregate Concentration Region Using Ultrasound Velocity Measurements. Sci. Rep. 2017, 7, 11. (45) Mojelsky, T. W.; Ignasiak, T. M.; Frakman, Z.; Mcintyre, D. D.; Lown, E. M.; Montgomery, D. S.; Strausz, O. P. Structural Features of Alberta Oil Sand Bitumen and Heavy Oil Asphaltenes. Energy Fuels 1992, 6, 83−96. (46) Zhou, X.; Zhang, Y.; Zhao, S.; Chung, K. H.; Xu, C.; Shi, Q. Characterization of Saturated Hydrocarbons in Vacuum Petroleum Residua: Redox Derivatization Followed by Negative-Ion Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry. Energy Fuels 2014, 28, 417−422.

K


Molecular Structure of Heavy Petroleum: Revealed by Molecular

Recommend Documents