Article pubs.acs.org/EF
Molecular Characterization of Polar Heteroatom Species in Venezuela Orinoco Petroleum Vacuum Residue and Its Supercritical Fluid Extraction Subfractions Linzhou Zhang, Zhiming Xu,* Quan Shi,* Xuewen Sun, Na Zhang, Yahe Zhang, Keng H. Chung, Chunming Xu, and Suoqi Zhao State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing 102249, People’s Republic of China S Supporting Information *
ABSTRACT: A Venezuela Orinoco petroleum vacuum residue (VR) was subjected to supercritical fluid extraction fractionation (SFEF) and separated into 13 extractable fractions and an unextractable end-cut. Detailed molecular composition of polar heteroatom species in the SFEF subfractions were determined by electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The SFEF subfractions were also subjected to high-temperature gas chromatography (GC) for their simulated distillation analysis, gel permeation chromatography (GPC) for their molecular distributions, and open column liquid chromatography for their saturates, aromatics, resins, and asphaltenes (SARA) compositions. In ESI FT-ICR analysis, the mass spectra showed that the mass range and maximum peak of the SFEF subfraction increased as the SFEF subfraction became heavier. Multifunctional group compounds, such as N1S1, N1S2, N1O1, and N2, show high relative abundance in heavier subfractions. The double bond equivalence (DBE) values and carbon numbers of all class species increased steadily as the SFEF subfraction became heavier. This indicated that the molecules in various SFEF subfractions are separated by their aromaticity and molecular weight. The SFEF end-cut could not be thoroughly characterized by ESI because of its low intensity, while basic species detected by positive-ion ESI were suppressed by a strong response of metal porphyrin species. Results from GPC and SARA compositional analysis show that the end-cut enriches most of the asphaltene in feedstock and has the highest apparent molecular size. reported as a supercritical solvent in other supercritical fluid extraction method.12,13 SFEF technology separates vacuum residues into about a dozen extractable fractions and one end-cut, which facilitates the compositional or reaction behavior study on heavy petroleum and its subfractions. In previous studies, various aspects of SFEF narrow subfractions have been investigated, such as hindered diffusion,14 hydroconversion,15 fluid catalytic creaking (FCC) product yields,16 solubility parameters,17 and sulfur species reactivity.18 Recently, the information on alkyl side chains19 and average structure20 has been described as well. However, because of the complex nature of heavy petroleum, there is still no “real molecular” level investigation on the SFEF subfractions. Their detailed molecular structure and diversity have not yet been fully understood. Recent advantages in Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) promote the study on detailed molecular composition of complex heavy fossil fuel and their property, which has promoted great progress in the field of “petroleomics”.21,22 From the prior works by Zhan and Fenn23 and Qian et al.,24,25 coupling electrospray ionization (ESI) with FT-ICR MS is proven to be a practical way to investigate the polar heteroatom species of
1. INTRODUCTION Heavy oil and bitumen have become important feedstock, because of the depleting conventional oil supply and limited amount of economic renewable energy. One major characteristic of heavy oil and bitumen is the high amount of nondistillable vacuum residua, which is enriched with heteroatoms, metals, and highly carbonized molecules. Hence, heavy oil and bitumen are challenging feedstock for refinery processes and more difficult to handle because of their high fouling propensity. Solvent deasphalting (SDA) is a mature refinery process that use light alkanes or their mixtures to separate heavy feedstocks into deasphalted oil (DAO) and bottom material. The separation of molecules is based on their solubility.1−8 The efficiency of solvent separation and DAO yield are dependent upon solvent type, amount of solvent, and process operating condition. Nevertheless, the conventional SDA has not reached the “maximum potential” as a heavy oil refinery process because of the low DAO yield.9 About a decade ago, the State Key Laboratory of Heavy Oil Processing at the China University of Petroleum developed the supercritical fluid extraction fractionation (SFEF),9 which allows for deep and clean separation of heavy hydrocarbons.9 The solubility of the supercritical fluids can be varied by adjusting solvent, operating pressure, and temperature. Low carbon number alkanes, such as propane, butane, and pentane, are usually used as a supercritical solvent because of their good solubility for petroleum-derived materials.10,11 Toluene was also © 2012 American Chemical Society
Received: June 6, 2012 Revised: August 12, 2012 Published: August 27, 2012 5795
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using the American Society for Testing and Materials (ASTM) D200711 standard. 2.2. High-Temperature Simulated Distillation. The test samples were subjected to high-temperature simulated distillation using the AC high-temperature SIMDIS analyzer (equipped with Agilent 6890N GC) using the AC HT-750 method. Cumulative yields as a function of the boiling point up to 750 °C of the VR sample and its SFEF subfractions were shown in Figure 2. The end-cut was not measured because of its poor volatility. 2.3. Gel Permeation Chromatography (GPC). Molecular size distributions of the VR sample and its SFEF subfractions were obtained using the Waters GPC515-2410 unit coupled with a refractive index detector. The chromatography column is Waters Styragel HT-5. The sample was diluted in tetrahydrafuran (THF) solvent at 1 mg/mL concentration. Considering the low injection concentration and the dilution by mobile phase, the effect of aggregation should be weakened in GPC experiment. Operation was under a 1 mL/min flow rate at 30 °C. 2.4. FT-ICR MS. The VR sample and its SFEF subfractions and the unextractable end-cut were subjected to FT-ICR MS analysis using a Bruker Apex Ultra FT-ICR mass spectrometer equipped with a 9.4 T superconducting magnet and an Apollo II electrospray ion source. Samples were dissolved in a blended toluene and methanol (4:6, v/ v) solvent at a concentration of 0.2 mg/mL, which was an ultralow concentration, indicating that the effect of aggregation should be ruled out. A total of 15 μL of aqueous solution of ammonium hydroxide (28−35 wt %) and 10 μL of formic acid were added for negative- and positive-ion ESI, respectively, to enhance molecular ionization. The typical conditions for negative-ion formation were 4.0 kV emitter voltage, 4.5 kV capillary column introduced voltage, and −320 V capillary column end voltage. The operating conditions for positive-ion formation were −3.0 kV emitter voltage, −3.5 kV capillary entrance voltage, and 320 V capillary column end voltage. For the VR sample, the key operating parameters were 250−1200 mass range and 4 M acquired data size. The operating condition of each SFEF subfraction was optimized on the basis of the mass spectrum intensity and peak distribution. The FT-ICR MS analysis of the non-extractable end-cut showed a low spectrum intensity and short cyclotron time. The acquired data size was set at 1 M. For extractable SFEF cut, the typical resolving power (m/Δm50%) at m/z 400 is ∼40 000. FT-ICR MS was internally calibrated with the N1 class homologous series. Mass spectrum peaks with a relative abundance greater than 5 times the standard deviation of the baseline noise were exported to a spreadsheet. Data analysis was performed using custom software. Compositional assignment of each peak was performed within 0.0015 Kendrick mass defect (KMD) tolerances. The detail of data processing could be found elsewhere.33,34
petroleum. There are various reports recently characterizing distillation or solvent separation fractions of petroleum.26−32 This work was aiming to give a detailed molecular investigation on the polar heteroatom species in SFEF subfractions. Both negative- and positive-ion FT-ICR MS was applied to describe structural variation of acidic and basic species during the SFEF procedure. Bulk property analysis was also performed to give full insight of these materials.
2. EXPERIMENTAL SECTION 2.1. Feedstock and SFEF. The feedstock was a petroleum vacuum residue (VR, 500 °C+ material) derived from Venezuela Orinoco heavy crude oil. A total of 13 extractable narrow fractions and a unextractable end-cut of VR sample (1 kg) were prepared by SFEF. The description and operating procedure of SFEF have been described elsewhere.9 Normal pentane was used as the supercritical solvent and operated in programming pressure with an increasing gradient of 1.0 MPa/h. Table 1 shows the yields of SFEF subfractions as a function of the SFEF extraction pressure.
Table 1. Extracted Pressure and Yield of Each Cut in Homemade SFEF Equipment cut number
extract pressure (MPa)
yield (wt %)
comment
1 2 3 4 5 6 7 8 9 10 11 12 13 end-cut
6.02 6.54 6.85 7.17 7.51 7.84 8.21 8.59 9.05 9.62 10.30 11.20 12.00 N/A
5.24 5.12 5.04 5.08 5.09 5.02 5.06 5.01 5.01 4.62 5.18 4.87 3.48 34.38
flowable flowable flowable flowable flowable flowable unflowable unflowable unflowable unflowable unflowable unflowable unflowable solids
The extractable SFEF subfraction summed to 63.82 wt % of VR, and the total mass balance of the experiment reached 98.2 wt %. About 1.8 wt % of feedstock remained in the extraction kettle and pipeline because of the high viscosity of feedstock. Five SFEF subfractions, SFEF1, SFEF4, SFEF7, SFEF10, and SFEF13, and the unextractable end-cut (their toluene solutions are shown in Figure S1 of the Supporting Information) were subjected to the bulk property analyses, such as density, Conradson carbon residue (CCR) content, and elemental analysis, as shown in Table 2. Saturates, aromatics, resins, and asphaltenes (SARA) compositional analysis was also performed
3. RESULTS AND DISCUSSION 3.1. Bulk Property. The feedstock of this study, VR of Venezuela Orinoco crude oil, is an ultraheavy petroleum
Table 2. Bulk Property of Venezuela VR and Its SFEF Subfractions elemental analysis C (wt %)
H (wt %)
S (wt %)
Nc (wt %)
Od (wt %)
Nie (wppm)
Ve (wppm)
CCRf (wt %)
density at 20 °Cg (g/cm3)
82.69 83.76 83.81 83.66 83.11 82.56 82.95
9.68 11.08 10.94 10.54 10.05 9.51 8.47
4.80 3.40 3.90 4.40 4.90 5.20 5.70
0.98 0.47 0.50 0.58 0.81 1.07 1.78
1.60 1.41 1.30 1.58 1.65 1.48 1.62
176 4.0 6.7 22.6 66.4 145 313
752 21.0 20.2 78.5 253 605 1383
26.19 4.61 7.76 12.13 18.39 28.80 49.28
1.0524 0.9746 0.9845 1.0066 1.0182 1.0472 0.4379h
a
feed SFEF1 SFEF4 SFEF7 SFEF10 SFEF13 end-cut
a
b
a
ASTM D5291 (flash EA 1112 analyzer). bASTM D5453 (Antek 7000 elemental analyzer). cASTM D5762 (Antek 7000 elemental analyzer). ASTM D5622 (flash EA 1112 analyzer). eASTM D5708 (Vista-PRO simultaneous ICP−OES). fASTM D189 (Shanghai Yutong Instrument YT30011). gASTM D1480 (pyonometer). hThe end-cut is a solid material, and the density is the stacking density.
d
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ICR MS was applied. Figure 2 shows the broadband negativeion mass spectra. The mass spectrum of VR ranged from m/z 250 to 1000, centered at m/z 600. The mass spectrum range and maximum peak of the SFEF subfraction increased as the subfraction became heavier. The most abundant peaks of the extractable SFEF subfraction varied from m/z 400 in SFEF1 to m/z 600 in SFEF13. The mass range of SFEF1 was from 250 to 700, and that of SFEF13 was from 300 to 1000. It is notable that mass spectra showed a discontinuity from the last extractable subfraction SFEF13 to the non-extractable end-cut. The low intensity indicated that the non-extractable end-cut was insufficiently ionized. Moreover, the cyclotron time (∼1 s) of FT-ICR MS for the end-cut was not long enough to achieve a high-resolution data acquisition. Because the end-cut has high sulfur content and high molecular weight, the resolving power is not high enough to distinguish the overlapping peaks. Hence, the data of the end-cut were not extensively analyzed. Figure 3 shows the close-up view of expanded mass spectra of the VR and its SFEF subfractions at m/z 438. Distinct disparity in composition among the SFEF subfractions and the end-cut was observed, indicating the effectiveness of SFEF heavy oil separation. In the VR, C32H40N1 and C30H32N1S1 negative ions were the most abundant. [C32H40N1]− [double bond equivalence (DBE) of 13 for the neural ion] was a highly dominant species in SFEF1; however, its content decreased dramatically in the heavier SFEF subfractions, and its dominancy was substituted by [C30H32N1S1]− in SFEF10 and [C33H28N1]− in SFEF13 and the end-cut. The mass peaks of [C28H24N1S2]− and [C31H20N1S1]− negative ions were suppressed by other peaks in the VR. After the light fractions of VR were removed, [C28H24N1S2]− and [C31H20N1S1]− can be observed in SFEF10, SFEF13, and the end-cut. Figure 4 is the isoabundance plots of DBE as a function of the carbon number for the pyrrole compounds in the VR and its SFEF subfractions. The pyrrole compounds in the VR varied over a wide range, with DBE of 9−21 and carbon numbers of 20−75. The most abundant of them was located at DBE of 13 and carbon number of 40. A progressive change in the DBE value and carbon number was observed in the extractable SFEF
feedstock containing high sulfur and nitrogen elements (4.80 and 0.98 wt %, respectively) with 1.0524 g/cm3 density at 20 °C. Bulk properties of the VR and its SFEF subfractions are listed in Table 2. After separation by SFEF, the C/H ratio and total nitrogen and sulfur elemental contents of subfractions show steady growth with extracted pressure and, moreover, a large difference in vanadium and nickel element contents is observed. Figure 1 shows the nominal boiling point distribution
Figure 1. Nominal boiling point distribution of Venezuela VR and its extractable SFEF subfractions.
of the Venezuela VR and extractable SFEF subfractions by the high-temperature simulated distillation method. A progression on boiling point of the SFEF series was observed. 3.2. Molecular Composition Characterized by Negative-Ion ESI FT-ICR MS. To investigate molecular composition of acidic and non-basic heteroatom species in Venezuela VR and its SFEF subfractions, negative-ion ESI FT-
Figure 2. Broadband negative-ion ESI FT-ICR mass spectrum of Venezuela VR and its SFEF subfractions. The overall mass peak and range of the spectra increased from SFEF1 to SFEF10. Mass ranges of SFEF13 and the end-cut do not change significantly. The signal density of the end-cut was very low, and it was analyzed in lower resolution. 5797
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class species was a unit higher that of the N1 class species. The N1S1 class species have an additional sulfur-containing group compared to the N1 class species. In petroleum, the most common sulfur-containing groups are sulfide (DBE of 0) and thiophene (DBE of 3). On average, the N1S1 class species have a higher DBE value than the N1 class species because of the contribution of the thiophene group. O2 class species should mainly be the carboxylic acids,35 which were another abundant species ionized by negative-ion ESI. Figure 5 is the isoabundance plots of DBE as a function of the carbon number for the O2 class species in the VR and its SFEF subfractions. A slight increase of DBE values among SFEF subfractions could be observed. Most of the O2 class species detected in negative-ion ESI FT-ICR MS are naphthenic acids. Different from the aromatic ring, the number of naphthenic rings do not form a significant impact on the polarity of the molecule. Thus, the DBE variation of the O2 class species is not significant during SFEF for Venezuela VR. The range of carbon numbers of the O2 class increased as the SFEF subfraction became heavier. The isoabundance plot showed that SFEF had a low relative abundance of high carbon number O2 class species. 3.3. Molecular Composition Characterized by Positive-Ion ESI FT-ICR MS. Positive-ion ESI selectively ionizes basic species, such as pyridines, sulfoxides, and metal porphyrin compounds.25,36 Figure 6 is the broadband positive-ion ESI FTICR mass spectra of the VR and its SFEF subfractions. The mass peaks marked by asterisks are identified as contaminants (emulsifying agent). Molecular weights of the basic species were increased slightly as the SFEF subfraction became heavier. The mass spectrum of the end-cut consisted of sparse peaks. Figure 7 shows the expanded mass scale spectra at m/z 500, revealing the enrichment of C37H42N1 positive ions and positive metal porphyrin compound ions ([C29H29N4O1V]+) in heavy extractable SFEF subfractions. Because of high responses of vanadium porphyrin species,36 only the vanadium porphyrin
Figure 3. Expanded negative-ion ESI FT-ICR mass scale spectrum at m/z 438.
subfraction series. The most significant difference between the light and heavy SFEF subfractions was the shift in DBE distribution: SFEF1 with DBE of 7−17 and SFEF13 with DBE of 13−22. DBE and carbon number variations of sulfur-containing pyrrole compounds (N1S1 class) among the SFEF series were similar to pyrrole compounds. Figure S2 of the Supporting Information is the isoabundance plots of DBE as a function of the carbon number for the N1S1 class species in the VR and its SFEF subfractions. Morever, the average DBE value of the N1S1
Figure 4. Plots of DBE as a function of the carbon number for N1 class species in Venezuela VR and its SFEF subfractions from negative-ion ESI FTICR mass spectra. 5798
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Figure 5. Plots of DBE as function of the carbon number for O2 class species in Venezuela VR and its SFEF subfractions from negative-ion ESI FTICR mass spectra.
Figure 6. Broadband positive-ion ESI FT-ICR mass spectrum of Venezuela VR and its SFEF subfractions. The mass peaks marked by asterisks are identified as contaminants (emulsifying agent).
subfractions were 2 units higher than those of pyrrole compounds analyzed in negative-ion mode. Composition of the positive-ion N1S1 class and N2 class species in the VR and its SFEF subfractions is shown in Figure S2 of the Supporting Information and Figure 9, respectively. Molecules in both classes contain at least one pyridine unit. Their trends in DBE and carbon number variations with extract pressure of those classes are similar to their N1 class analogues. 3.4. Relative Abundance of Heteroatom Species. Figure 10 shows the distributions of various class species in the VR and its SFEF subfractions from negative-ion ESI FTICR MS. A total of 13 class species were identified from the
peak was visible in the mass spectrum of the end-cut. The characterization and detailed discussion on metallic compounds will be addressed in our future publication. Figure 8 is the isoabundance plots of DBE as a function of the carbon number for the basic nitrogen species in the VR and its SFEF subfractions. Because amines are rarely present in crude oil,31 the basic nitrogen compounds are pyridine derivative compounds. The minimum DBE value for pyridine compounds (N1 class) in the VR was 5, which refers to the core structure of a pyridine unit plus a naphthenic ring. DBE values of the most abundant pyridine in the extractable SFEF 5799
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multifunctional group compounds, such as N2, N1S1, and N1S2 class species. Pyridine and sulfoxide units are the known function groups in positive-ion ESI (metal porphyrins are not under consideration). As shown in Figure 11, the complexity nature of heavy oil results in 11 classes of measured molecules in combination with other functional groups, which are N1, N1O1, N1O1S1, N1O2, N1S1, N1S2, N2, N2O1, O1S1, and O1S2. The relative abundance of N1 class species was 55% in SFEF1 and decreased gradually to 20% in SFEF13. The relative abundance of multi-heteroatom class species had undergone substantial surges as the subfraction became heavier. In positive-ion ESI, the O1S1 class species were sulfoxide compounds and the O1S2 class species were sulfoxide derivatives, which were different from the negative-ion ESI mode (in negative-ion ESI, O1S1 and O1S2 class species are phenol compounds added with one and two sulfur functional groups, respectively). The relative abundances of those class species were quite low (less than 7% in total), but a clear downward tendency could be observed. 3.5. DBE Distribution in SFEF Subfractions. The N1 class species are the most abundant compounds present in the negative- and positive-ion ESI FT-ICR mass spectra of the VR and its SFEF subfractions. Figure 12 showed the scaled relative abundance of pyrrole and pyridine compounds in the SFEF subfractions as a function of their DBE value. The DBE distribution data for each SFEF subfraction showed a bellshaped distribution curve. It is clear that, as the SFEF subfraction became heavier, the DBE distribution curve shifted to the right. The DBE distribution curve of pyridine derivative compounds in SFEF13 showed a considerable amount of low DBE pyridine compounds, resulting in an offset of the DBE distribution curve at DBE of 5−15. As a precaution, the FTICR MS condition was checked to avoid the bond dissociation of ions. The low DBE pyridine compounds could be the components of a lighter SFEF subfraction, which was retained
Figure 7. Expanded mass scale spectrum of positive-ion ESI FT-ICR MS at m/z 500.
mass spectra: N1, N1O1, N1O2, N1S1, N1S2, N2, N2S1, N2O1, O1, O1S1, O1S2, O2, O2S1, and O2S2. In the light SFEF subfractions, single functional group compounds, such as N1 (pyrrole derivative compounds) and O2 (carboxylic acids), were dominant. Heavier SFEF subfractions were enriched with
Figure 8. Plots of DBE as function of the carbon number for N1 class species in Venezuela VR and its SFEF subfractions from positive-ion ESI FTICR mass spectra. 5800
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Figure 9. Plots of DBE as a function of the carbon number for N2 class species in Venezuela VR and its SFEF subfractions from positive-ion ESI FTICR mass spectra.
aromatic and the physical properties, such as the boiling point of hydrocarbons, are dependent upon aromaticity and aromatic ring number,37,38 it is reasonable to expect that the aromaticity of compounds in feedstock plays an important role in SFEF operation. On the other hand, the variation in class of polar heteroatom compounds could also be attributed to the growth of aromaticity. Those classes with growing relative abundance against extracted pressure, such as N1O1, N1S1, and N1S2, in both negative- and positive-ion ESI FT-ICR MS are the combination of pyrrole, phenol, and sulfur-containing units. Pyrrole and phenol units are both aromatic structural groups. There was also a study that showed that about 65−80% of sulfur-containing functional groups are thiophene units.18 In the assignment of those multi-aromatic functional group compounds during SFEF separation, they will have a higher probability to go into high aromatic fractions. 3.6. Polar Species in the End-cut. The ionization of polar heteroatom compounds in the end-cut was hindered in ESI FTICR MS analysis. This unextractable end-cut, which is a solid material, accounted for 35 wt % of the VR sample. Figure 13 shows the SARA composition of SFEF1, SFEF4, SFEF7, SFEF13, and the end-cut. Saturates were dominant in SFEF1. Aromatics were about 60 wt % in SFEF4, SFEF7, and SFEF10. Resins were dominant in SFEF13 at 60 wt %. From the SARA analysis, it is expected that the polarity of the SFEF subfraction increased as the SFEF subfraction became heavier. The end-cut had the highest polarity because of the highest asphaltene content among all SFEF subfractions. However, from the molecular point of view, “polar” and “heavy” are not clear definitions. In fact, there were a number of controversies over the molecular configuration of heavy oil fractions.39−41 Extrapolated from extracted SFEF subfractions, we infer that heteroatom molecules in the end-cut must be with high aromaticity and molecular weight. The multifunctional group class should be dominant in the end-cut, contributing mainly to the abundance of the heteroatom element.
Figure 10. Class distribution of negative-ion mode ESI FT-ICR MS in Venezuela VR and its extractable subfractions.
Figure 11. Class distribution of positive-ion ESI FT-ICR MS in Venezuela VR and its extractable subfractions.
in the SFEF extractor and flushed out along with the last extractable SFEF subfraction. However, the overall shapes and peaks of the SFEF13 DBE distribution are still under the same inclination among other SFEF subfractions. From the SFEF subfraction yield data in Table 1 and the DBE distribution curve of each SFEF subfraction, it can be estimated that the DBE values of nitrogen compounds increased by 2 DBE as the SFEF extraction pressure increased by 1 MPa. Also, because the heavy SFEF subfractions are highly 5801
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Figure 12. Scaled relative abundance distribution of DBE for N1 class species in extractable SFEF subfractions. For each subfraction, the DBE distribution was rescaled by its highest point.
appear in early retention time. All extractable SFEF subfractions appeared after 26 min. The GPC peak of the extractable SFEF subfraction shifted to the left as the SFEF subfraction became heavier. The result is in agreement with the MS analysis shown in Figures 2 and 7. Molecular size and size dispersity of the endcut were significantly higher than extractable SFEF subfractions.
4. CONCLUSION Molecular composition of polar species in Venezuela petroleum VR and its supercritical fluid extraction subfractions was investigated using ESI FT-ICR MS. Peaks and mass ranges of mass spectra grow slightly with extracted pressure. Heavy SFEF subfractions have high aromaticity, resulting in lower abundance of saturate carbon-related class, such as O2 and O2S1. The relative abudance of the multifunctional group class, such as N1S1, N1S2, and N2, is growing gradually with SFEF pressures. The DBE distributions of N1 species of SFEF subfractions are bell-shape-like and share similar ranges. Around a 1 MPa extraction pressure increment leads to a 2 DBE value growth of these species in the system. In addition, an apparent increase in the carbon number among SFEF subfractions was observed. Low ionization efficiency hindered the measurement of the end-cut. Extrapolated from extracted subfractions, this asphaltene-rich fraction should have a higher molecular weight with more multifunctional group class.
Figure 13. SARA compositional analysis result of SFEF subfractions of Venezuela VR.
GPC is a practice method to measure the molecular size distribution of hydrocarbons.40,42 Figure 14 shows the GPC result of the VR and its subfractions. Molecules with a large size
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ASSOCIATED CONTENT
S Supporting Information *
Toluene solution of SFEF subfraction (Figure S1) and plots of DBE as function of the carbon number for N1S1 class species in Venezuela VR and its SFEF subfractions from negative- and positive-ion ESI FT-ICR mass spectra (Figures S2 and S3). This material is available free of charge via the Internet at http://pubs.acs.org.
Figure 14. GPC chromatograms of Venezuela VR and its SFEF subfractions. 5802
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AUTHOR INFORMATION
Corresponding Author
*Telephone: +86-10-8973-3743 (Z.X.); +86-10-8973-3738 (Q.S.). Fax: +86-10-6972-4721 (Q.S.). E-mail:
[email protected]. cn (Z.X.);
[email protected] (Q.S.). Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work was supported by the National Basic Research Program of China (2010CB226901) and the Union Fund of the National Natural Science Foundation of China (NSFC) and the China National Petroleum Corporation (CNPC) (U1162204), and the NSFC Fund (21176254). The authors thank Sha Chen for preparing the SFEF samples.
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dx.doi.org/10.1021/ef3009663 | Energy Fuels 2012, 26, 5795−5803
