Characterization of Petroleum Heavy Oil Fractions Prepared by

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Characterization of Petroleum Heavy Oil Fractions Prepared by Preparatory Liquid Chromatography with Thin-Layer Chromatography, High-Resolution Mass Spectrometry, and Gas Chromatography with an Atomic Emission Detector Eunkyoung Kim,†,‡ EunJi Cho,‡ Serah Moon,† Joo-Il Park,§ and Sunghwan Kim*,‡,∥ †

Institute of Technology, SK Innovation, Daejeon 305-712, Republic of Korea Department of Chemistry, Kyungpook National University, Daegu 702-701, Republic of Korea § Petroleum Research Center, Kuwait Institute for Scientific Research, P.O. Box 24885, Safat, 13109 Kuwait ∥ Green-Nano Materials Research Center, Daegu 702-701, Republic of Korea ‡

S Supporting Information *

ABSTRACT: In this study, a preparatory-scale fractionation method was developed. To verify the effectiveness of this method, an oil sample was fractionated into five fractions, referred to as saturate, aro1, aro2, polar1, and polar2; these fractions were completely characterized by thin-layer chromatography−flame ionization detection (TLC−FID), field desorption (FD) and (+) atmospheric pressure photoionization (APPI) high-resolution mass spectrometry (HR-MS), and gas chromatography with an atomic emission detector (GC−AED). TLC−FID analysis was used to compare the results obtained by the fractionation method to those obtained from the conventional saturates, aromatics, resins, and asphaltenes (SARA) method. FD−MS was employed to characterize the hydrocarbon class compounds in the saturate and aro1 fractions. As observed from the FD−MS spectra, non-aromatic hydrocarbon compounds were abundant in saturates, while mono- and diaromatic compounds were abundant in the aro1 fraction. This result is in good agreement with those obtained by HR-MS. (+) APPI HR-MS analysis of fractions showed that aromaticity increases from saturates to the polar1 fraction but decreases in the polar2 fraction. Heteroatom class distributions investigated by (+) APPI HR-MS showed that non-basic nitrogen compounds were abundant in polar1, while non-aromatic sulfur compounds were abundant in the polar2 fraction. From the results obtained by the GC−AED analysis of fractions, nickel porphyrin compounds were concentrated in the polar1 fraction. Hence, the combined results clearly demonstrate that the fractionation method is effective for isolating fractions on a preparative scale.

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two-dimensional nuclear magnetic resonance (2D NMR).15 The information provided by HPLC, HR-MS, and 2D NMR can be effectively combined for verifying the information obtained from each technique.15 However, it is also very clear from that previous study that analytical-scale HPLC demonstrates a limitation, in that a sufficient amount of sample is required for various analytical techniques.15 For this purpose, the analyticalscale HPLC run and sample collection, which require approximately 1.5 h for completion, have to be repeated approximately 20−30 times to obtain a sufficient amount of sample for 2D NMR analysis. In addition, additional time is required for evaporating the collected samples and preparing for subsequent analysis. To overcome this limitation, preparatory-scale sample preparation methods have been developed.16−21 However, saturates, aromatics, resins, and asphaltenes (SARA) separation has been typically performed,14,22,23 and more detailed ring-type separation has not been widely performed with preparatory-scale separation.24 In this study, heavy crude oil was fractionated by a preparatory-scale liquid chromatography method and the fractions thus obtained were analyzed by various analytical

INTRODUCTION Crude oil is an important source of energy for modern society; hence, studies devoted to the understanding of its chemical compositions have been reported.1 Traditionally, gas chromatography−mass spectrometry (GC−MS) has been one of the important tools for investigating the compositions of oils. However, gas chromatography demonstrates a limitation, in that heavy components of crude oils with high polarity and/or molecular weight (MW > 400) cannot be analyzed. For overcoming this limitation, high-resolution mass spectrometry (HR-MS) combined with various ionization sources and data interpretation methods has been successfully applied for studying the heavy components of oils.2−4 On the other hand, crude oil is an extremely complex material; thus, clearly, a single technique cannot resolve its complexity. In other words, data obtained from different analytical techniques have to be combined to better understand complex crude oil.2 In this regard, it is imperative to develop and apply chromatographic techniques that can separate crude oil compounds into groups exhibiting similar chemical characteristics.5−12 High-performance liquid chromatography (HPLC) has been successfully combined with HR-MS for studying crude oils.13,14 Previously, fractions obtained from ring-type HPLC separation have been analyzed by the combination of HR-MS and © XXXX American Chemical Society

Received: February 4, 2016 Revised: March 7, 2016

A

DOI: 10.1021/acs.energyfuels.6b00296 Energy Fuels XXXX, XXX, XXX−XXX

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Energy & Fuels

MS, Bruker Daltonics, Billerica, MA) was used for analyzing the heavy fractions. Samples were dissolved in toluene at 0.05 wt %. Typically, toluene is used as a dopant for improving the efficiency of photoionization. Diluted samples were directly injected using a syringe pump at a flow rate of 300 μL/h. Nitrogen was used as a drying, nebulizing gas for the ionization source. For APPI analysis, the nebulizing temperature was set to 380 °C, with a flow rate of 3.0 L/min, and the drying gas temperature was set to 200 °C, with a flow rate of 2.0 L/min. Ionized samples were accumulated in the collision cell for 0.2 s and transferred to a ion cyclotron resonance (ICR) cell with a time-of-flight (TOF) window of 2 ms. The ions were trapped in the ICR cell with a sidekick voltage of 8 V. At least 100 scans were accumulated for increasing the signal-tonoise ratio. In total, 4 × 106 data points were recorded. Spectra were interpreted using the Statistical Tool for Organic Mixture Spectra software with an automated peak picking algorithm for more reliable and faster results.26,27 The threshold for peak picking was a signal-to-noise ratio greater than 5.0. After peak peaking and internal calibration, molecular formulas were assigned within an error range of 1 ppm. Normal conditions for petroleum data (CcHhNnOoSs, where c is unlimited, h is unlimited, 0 ≤ n ≤ 5, 0 ≤ o ≤ 5, and 0 ≤ s ≤ 4) were used for these calculations. Double bond equivalence (DBE) represents the number of rings plus the number of double bonds in a given molecular formula. DBE values can be calculated using the following equation:

techniques, such as thin-layer chromatography−flame ionization detection (TLC−FID), gas chromatography, and HR-MS. The data thus obtained were comprehensively combined for characterizing the chemical compositions at the molecular level.

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EXPERIMENTAL SECTION

Materials. Atmospheric residue (AR) is the oil obtained from the bottom of the atmospheric distillation unit for crude oil. An AR sample was provided by SK Innovation Co., Ltd. (Daejeon, Korea). Table 1

Table 1. Macroproperties of the AR Sample Used in This Study API gravity (deg) 11.6

specific gravity S (wt %) N (wt ppm) Ni (wt ppm) V (wt ppm) 0.989

4.55

2,240

22.3

67.8

summarizes its bulk properties, such as American Petroleum Institute (API) gravity, sulfur content, nitrogen content, and metal content. Each test method employed for the measurement of bulk properties has been described in the Supporting Information. AR maltene samples were prepared by extraction using hot heptane by the ASTM D3279 method.25 HPLC-grade solvents were purchased from Burdick and Jackson (Morris Plains, NJ) and used without further purification. Chromatography. Samples were separated on a CombiFlash Rf liquid chromatography [medium-pressure liquid chromatography (MPLC)] system purchased from Teledyne Isco, Inc. (Lincoln, NE). A normal-phase silica (80 g) column purchased from Teledyne Isco, Inc. was used. Then, 0.1−0.3 g of the AR maltene samples was dissolved in 3 mL of hexane and loaded onto the silica column. HPLC-grade hexane, toluene, ethyl acetate, and methanol were used as eluting solvents. Table 1S of the Supporting Information lists the detailed solvent program used for separation. Briefly, a mixture of hexane, toluene, hexane, ethyl acetate, and methanol were sequentially eluted. MPLC conditions, such as column size, flow rate, and elution time, were optimized by trial and error. The elution time between eluting solvents was decided as 7 min, because each solvent took approximately 6 min to be eluted from the separating column at a flow rate of 25 mL/min. An evaporative light scattering detector (ELSD, Teledyne Isco, Inc., Lincoln, NE) and ultraviolet (UV) detector (Teledyne Isco, Inc., Lincoln, NE) between 200 and 360 nm were employed. Two wavelengths can be simultaneously monitored using the UV detector. ELSD conditions were used under default conditions with a nitrogen gas flow of 60 psi, a spray chamber temperature of 35 °C, a drift tube temperature of 45 °C, and an optical cell temperature of 45 °C. The eluents from the column were fractionated using a fraction collector. The solvent of each fraction was evaporated by vacuum evaporation, and the net oil samples thus recovered were weighed. Thin-Layer Chromatography. TLC−FID made by Iatroscan MK-6S (Misthuibish, Japan) and silica chromarods (Misthuibish, Japan) were used for the characterization of AR maltene and its MPLC fractions. A total of 10 silica rods were analyzed at a time for ensuring the reproducibility of data. First, AR maltene and each MPLC fraction were diluted to a 0.2% solution in methylene chloride. Next, 1 μL of the diluted samples was spotted on each TLC silica rod and analyzed. After drying the dilution solvents for 3 min, hexane was eluted up to 10 cm and dried for removing the residual hexane for 6 min. Next, toluene was eluted up to 4 cm and dried for 6 min. Methylene chloride with 5% methanol was eluted up to 2 cm and dried for approximately 4 min. Mass Spectrometry. A JMS-T100GC FD-TOF MS (Jeol, Japan) was employed for the characterization of the first two fractions. The samples were diluted with hexane to approximately 0.1 wt %. The dissolved samples were applied onto a field desorption (FD) emitter using a gastight syringe (Hamilton, Reno, NV). The FD emitter was inserted into the ion source of the mass spectrometer near the extraction electrode. The voltage at the extraction electrode was set at 8 kV. The lenses at the ion source were tuned by monitoring the acetone signal. The ion source temperature was maintained at 50 °C. Atmospheric pressure photoionization (APPI) coupled with 7 T Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR

(1)

DBE = c − h/2 + n/2 + 1

for elemental formulas of CcHhNnOoSs. Gas Chromatography with an Atomic Emission Detector (GC−AED). GC−AED analysis was conducted using a 7890 gas chromatography system with a JAS 2390 atomic emission detector and DB-1 (J&W) column. The gas chromatograph was equipped with a programmable high-temperature vaporization (PTV) inlet. Emission wavelengths of 181, 193, and 301 nm were used for sulfur, carbon, and nickel, respectively.28,29 The retention time of the chromatogram was converted into the boiling temperature by referring to the boiling temperature and retention time of the n-paraffin mixture. The initial boiling temperatures were between 300 and 400 °C, and the final boiling temperature was around 740 °C. All samples were diluted in methylene chloride as 20 wt %. The experimental conditions of GC− AED employed herein were the same as those previously reported.28,29

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RESULTS AND DISCUSSION Normal-Phase MPLC Separation of AR Maltenes. Figure 1 shows a typical MPLC−ELSD chromatogram of the

Figure 1. MPLC−ELSD spectrum of an AR maltene.

AR maltene sample. The total elution time was 50 min, and the elution solvents were collected into five fractions, referred to as saturate, aro1, aro2, polar1, and polar2 fractions, respectively. The first peak eluted by hexane was the saturate fraction, which B


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Energy & Fuels was collected at the valley between the first and second peaks of the ELSD chromatogram. The aro1 group was collected from the end of the saturate to the end of elution using 5% toluene. The aro2 fraction was eluted using 30% toluene. The polar1 group was eluted using 100% toluene. The polar2 group was eluted using ethyl acetate and methanol. Figure 1S of the Supporting Information shows a flowchart explaining the elution program. The masses of each fraction were determined after evaporating the eluting solvents under vacuum. The weight recovery rate of MPLC separation was greater than 94%, as compared to the weight of the sample loaded on the column. Table 2 shows the weight percent distribution of the fractions obtained from the AR sample. Analyses were conducted 3 times, with the relative standard deviation shown in the table.

To check the effectiveness of the MPLC separation, fractions obtained from MPLC separation were analyzed with TLC−FID. Figure 2 shows the comparison between the results obtained from the MPLC separation and those obtained from the unfractionated sample. TLC−FID is one of the conventional techniques employed for investigating the SARA content of oils.30−34 The MPLC saturate fraction was in good agreement with the first peak of the TLC−FID chromatogram. Moreover, the aro1 and aro2 fractions were also in agreement with the aromatic fraction observed in TLC−FID. Polar1 and polar2 fractions from MPLC separation were in good agreement with the polar fraction obtained from TLC−FID. The polar1 fraction eluted using 100% toluene contained a small amount of aromatics, with the predominance of polar resin compounds. Further compositional analysis indicates a difference between the polar components in the polar1 and polar2 fractions. A detailed description of the difference is provided in the latter section. Characterization with Mass Spectrometry. To further characterize the saturate and aro1 fractions, FD-TOF MS was employed. Panel 1 of Figure 3 shows the FD-TOF MS spectra of the saturate and aro1 fractions. Panel 2 of Figure 3 shows the extended FD-TOF MS spectra. The saturate fraction was mainly composed of hydrocarbon (HC) class compounds. The HC class implies that the components are composed of only carbon and hydrogen and do not contain heteroatoms, such as oxygen, nitrogen, and sulfur. The assigned formulas and DBE values of the peaks are highlighted in the figure. The peak with DBE = 0 was the most abundant in the saturate fraction, but

Table 2. Weight Percent Distribution of Fractions Obtained by the Preparatory Fractionation Methoda

saturate aro1 aro2 polar1 polar2 total recovery

first trial (%)

second trial (%)

third trial (%)

26.4 22.0 27.4 9.6 9.3 94.7

24.5 22.4 30.0 11.2 11.0 99.1

26.1 23.1 29.6 10.8 9.9 99.5

average (%) 25.7 22.5 29.0 10.5 10.1 97.7

(±3.9) (±2.4) (±4.9) (±7.8) (±8.4) (±2.7)

a

Triplicate experiments were conducted, and the average and standard deviation are listed.

Figure 2. TLC−FID chromatograms of AR maltene and its MPLC fractions. C


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Figure 3. (1) Full-range FD-TOF MS spectra of AR saturate (top) and aro1 (bottom) fractions, (2) extended FD-TOF MS spectra of AR saturate (top) and aro1 (bottom) fractions in the range between m/z 440 and 500 (right column), and (3) DBE distribution observed from the saturate (left) and aro1 (right) fractions.

The decrease of the mass defect shows that the aromaticity of compounds in the fraction increases from the aro1 to polar1 fractions. Figure 4c shows the class distributions of the analyzed fractions. In the graph, the S1 class represents the compounds containing one sulfur atom and an unspecified number of hydrogens and carbons. The notations for the other classes can be similarly interpreted. HC, S1, N1, S2, N1O1, O1S1, O1, and N1S1 were the major classes observed by (+) APPI MS. The S1 class compounds were abundant in the aromatic and polar fractions and most abundant in the first two of the aromatic fractions. Relatively small abundance of the S1 class was observed in the saturate fraction. Typically, very low sulfur contents were observed in the saturate fraction, and the existence of the S1 class could indicate the existence of aromatic compounds in the saturate fraction. However, GC atomic emission spectroscopy (AES) data described in the later section of this paper (refer to Table 2S of the Supporting Information) showed that only a small (1−2%) sulfur emission signal were observed in the saturate fraction compared to the other fractions. Therefore, it was concluded that a negligible amount of aromatics existed in the saturate fraction. The N1 and oxygen-containing class compounds were the most abundant in the polar fractions but not in the saturate and aromatic fractions. For example, the saturate fraction contained a small content of N1 and N1O1 class compounds in the saturate and aromatic fractions compared to polar fractions (refer to Figure 4b). The relative abundance of the HC class decreased

the peak with DBE = 4 was the most abundant in the aro1 fraction. To further examine the DBE distribution, plots showing the overall DBE distribution of the saturate and aro1 fractions observed by FD-TOF MS are shown in panel 3 of Figure 3. The DBE of the HC class in the saturate fraction mainly ranged between 0 and 4, and compounds with a DBE value of 0 or 1 were the most abundant. The DBE value of a benzene ring is 4; hence, the abundance of compounds with DBE values less than 4 clearly indicates that the saturate fraction is mostly composed of saturated and/or naphthenic compounds. In case of the aro1 fraction, compounds with a DBE value of 4 were the most abundant, implying that the aro1 fraction is mainly composed of compounds with a monoaromatic ring. Figure 4 shows the spectra of the fractions analyzed by positive-mode APPI FT-ICR MS. Figure 4a shows the broadband and expanded spectra. Peaks with m/z values up to 1000 were observed in the spectra. Table 3 lists the average molecular weight values as calculated using eq 2. The molecular weight distribution observed by FT-ICR MS did not significantly change among the fractions. average molecular weight =

∑ (intensity × molecular weight) ∑ intensity

(2)

In the expanded spectra shown in Figure 4b, the mass defects of the peaks in aro1 to polar1 decreased for the latter fractions. D


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Figure 4. (a) Broadband (+) APPI FT-ICR mass spectra (left column), (b) expanded spectra in the range between m/z 456 and 459 (right column), and (c) compound class distributions of the fractions.

fraction started at 4, which is in good agreement with the FD-TOF data shown in Figure 3. The compounds with a DBE value greater than 4 were also observed in the aro1 fraction. Previously, the compounds with high DBE values in ring-type separation were attributed to compounds with an aromatic ring and saturated cyclic rings by the combined interpretation of NMR and FT-ICR MS data.15 The DBE values of the HC class in the aro2 fraction was mainly above 7, implying that aro2 is composed of polyaromatics with greater than two aromatic rings because naphthalene has a DBE value of 7. The HC class in the polar1 fraction had DBE values mainly greater than DBE 15, implying that the compounds contain a higher number of aromatic rings than the aro1 fraction. Figure 5b shows the carbon number versus DBE distributions of the S1 class of the aro1, aro2, polar1, and polar2 fractions. In the saturate fraction, the S1 class was a minor component. The DBE distribution of the value of the aro1 fraction started at 6, suggesting that benzothiophene derivatives are abundant in the aro1 fraction. In the case of the aro2 fraction, the DBE distribution started at 9, which was in good

Table 3. Average Molecular Weight (Mn) Calculated from the (+) APPI FT-ICR Mass Spectra of the Fractions Mn saturate aro1 aro2 polar1 polar2

436 483 472 465 447

from the aro to polar fractions. The overall class distribution shown in Figure 4c was in good agreement with that reported previously.15 In the previous study, ring-type separation was performed with HPLC, and the same trend of class distribution described above was observed from a sulfurrich oil sample.15 To further characterize these fractions, DBE versus carbon number plots of HC, S1, and N1 classes were generated (Figure 5). For the HC class compounds shown in Figure 5a, the DBE distribution clearly increased from the saturate to polar1 fractions. The DBE distribution of the HC class in the aro1 E


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Figure 5. Carbon number versus DBE distribution of the (a) HC class, (b) S1 class, and (c) N1 class of the studied fractions.

DBE values less than 4 were abundant. Hence, it was concluded that non-aromatic S1 class compounds, such as sulfide compounds, are abundant in the polar2 fraction.

agreement with the DBE value of dibenzothiophene. In the polar2 fraction, the DBE value of the S1 class compounds was lower than those of the aro fractions. In particular, peaks with F


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Figure 6. GC−AED chromatograms obtained showing the distribution of (a) carbon, (b) sulfur, and (c) nickel in the fractions.

Figure 5c shows the carbon number versus DBE distributions of the N1 class of polar1 and polar2 fractions. Also shown in the figure are the DBE distribution bar plots. The data obtained from only two fractions were shown in the figure because the N1 class was only abundant in those two fractions. The DBE value of the N1 class of the polar1 fraction started from 9, which is in agreement with the DBE value of carbazole.35,36 In addition, mostly molecular ions were observed. Previously, molecular ions were predominantly observed from nitrogen compounds having a carbazole core structure.37,38 Hence, it was concluded that the N1 class compounds observed in the polar1 fraction contain non-basic nitrogen. The DBE value of the N1 class in the polar2 fraction started from 4.39 Protonated ions were significantly more abundant than those in the polar1 fraction. Hence, it was concluded that nitrogen compounds in the polar2 fraction are mostly basic nitrogen, such as pyridine derivatives.35 Hence, the N1 class distribution shows that the current method is effective for separating non-basic and basic nitrogen compounds. GC−AED Analysis. The fractions were analyzed with GC−AED, and Figure 6 shows the results. Panels a and b of Figure 6 show the emission chromatograms of carbon and sulfur, respectively. The carbon data showed that the elution times (and, hence, elution temperature) of fractions were similar to each other (Figure 6a). The elution time of compounds observed with GC is well-known to be related to the boiling point and molecular weight of the compounds.5 Hence, the data suggest that the molecular weight distribution of the fractions is not significantly different, which implies that separation described herein is based on structures and functional groups but not the molecular weight of compounds. This interpretation is in good agreement with FT-ICR MS, where the average molecular weights were similar among the fractions (refer to Table 3).

Table 2S of the Supporting Information lists the peak area of sulfur compounds obtained from each fraction. The peak area from sulfur was almost 100 times less abundant in the saturate fraction. This result is in good agreement with the class distribution shown in Figure 4c. The sulfur class compounds observed by FT-ICR MS were the least abundant in the saturate fraction. Neutral sulfur compounds, such as benzothiophene and dibenzothiophene, are well-known to be eluted in the aromatic fractions.5 Notably, the peak areas of the aro1 and aro2 fractions were higher than those of the polar1 and polar2 fractions. This result is in good agreement with the class distribution observed by (+) APPI FT-ICR MS (refer to Figure 4c). Nickel compounds in the fractions were examined by GC−AED. Figure 6c shows the chromatograms for nickel. Nickel-containing compounds were the most abundant in the polar1 fraction. The list of peaks observed by (+) APPI FT-ICR MS was examined, and the m/z values were in agreement with those of the nickel porphyrins previously reported.40,41 Table 4 lists the m/z values. From the results obtained by GC−AED and (+) APPI FT-ICR MS, the current separation method is effective for isolating nickel-containing compounds. Table 4. Nickel Porphyrin Peaks Observed by (+) APPI FT-ICR MS in the Polar1 Fraction

G

calculated mass

assigned formula

measured mass

mass error (mDa)

mass error (ppm)

463.14274 477.15839 491.17404 505.18969 519.20534 533.22099 547.23664

C27H25N4Ni C28H27N4Ni C29H29N4Ni C30H31N4Ni C31H33N4Ni C32H35N4Ni C33H37N4Ni

463.14252 477.15793 491.17352 505.18943 519.20484 533.22042 547.23608

−0.22 −0.46 −0.52 −0.26 −0.50 −0.57 −0.56

−0.48 −0.96 −1.06 −0.51 −0.96 −1.07 −1.02


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(5) Altgelt, K. H.; Boduszynski, M. M. Composition of Heavy Petroleums. 3. An Improved Boiling Point-Molecular Weight Relation. Energy Fuels 1992, 6, 68−72. (6) Nocun, M.; Andersson, J. T. Argentation chromatography for the separation of polycyclic aromatic compounds according to ring number. J. Chromatogr. A 2012, 1219, 47−53. (7) Hsu, C. S.; Dechert, G. J.; Robbins, W. K.; Fukuda, E. K. Naphthenic Acids in Crude Oils Characterized by Mass Spectrometry. Energy Fuels 2000, 14, 217−223. (8) Robbins, W. K. Quantitative Measurement of Mass and Aromaticity Distributions for Heavy Distillates 1. Capabilities of the HPLC-2 System. J. Chromatogr. Sci. 1998, 36, 457−466. (9) Gole, A.; Andersson, J. T. Group-Type Separation of Nitrogen Containing Aromatic Compounds in Coal Tar Pitch on a Hafnium Modified Silica HPLC Phase. Polycyclic Aromat. Compd. 2015, 35 (1), 129−142. (10) Molnárné Guricza, L.; Schrader, W. Electrospray ionization for determination of non-polar polyaromatic hydrocarbons and polyaromatic heterocycles in heavy crude oil asphaltenes. J. Mass Spectrom. 2015, 50 (3), 549−557. (11) Loegel, T. N.; Danielson, N. D.; Borton, D. J.; Hurt, M. R.; Kenttämaa, H. I. Separation of asphaltenes by reversed-phase liquid chromatography with fraction characterization. Energy Fuels 2012, 26 (5), 2850−2857. (12) Cho, Y.; Na, J.-G.; Nho, N.-S.; Kim, S.; Kim, S. Application of saturates, aromatics, resins, and asphaltenes crude oil fractionation for detailed chemical characterization of heavy crude oils by Fourier transform ion cyclotron resonance mass spectrometry equipped with atmospheric pressure photoionization. Energy Fuels 2012, 26 (5), 2558−2565. (13) Sim, A.; Cho, Y.; Kim, D.; Witt, M.; Birdwell, J. E.; Kim, B. J.; et al. Molecular-level characterization of crude oil compounds combining reversed-phase high-performance liquid chromatography with off-line high-resolution mass spectrometry. Fuel 2015, 140, 717− 723. (14) Gaspar, A.; Zellermann, E.; Lababidi, S.; Reece, J.; Schrader, W. Characterization of Saturates, Aromatics, Resins, and Asphaltenes Heavy Crude Oil Fractions by Atmospheric Pressure Laser Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry. Energy Fuels 2012, 26 (6), 3481−3487. (15) Kim, D.; Jin, J. M.; Cho, Y.; Kim, E.-H.; Cheong, H.-K.; Kim, Y. H.; et al. Combination of ring type HPLC separation, ultrahighresolution mass spectrometry, and high field NMR for comprehensive characterization of crude oil compositions. Fuel 2015, 157, 48−55. (16) Radke, M.; Willsch, H.; Welte, D. H. Preparative Hydrocarbon Group Type Determination by Automated Medium Pressure Liquid hromatography. Anal. Chem. 1980, 52, 406−411. (17) Desbene, P. L.; Lambert, D. C.; Richardin, P.; Huc, A. Y.; Boulet, R.; Basselier, J.-J. Preparative Fractionation of Petroleum Heavy Ends by Ion Exchange Chromatography. Anal. Chem. 1984, 56, 313−315. (18) Carbognani, L.; Izquierdo, A. Preparative and automated compound class separation of Venezuelan vacuum redisua by Highperformance liquid chromatography. J. Chromatogr. 1989, 484, 399− 408. (19) Carbognani, L.; Izquierdo, A. Preparative compound class separation of heavy oil vacuum residua by high performance liquid chromatography. Fuel Sci. Technol. Int. 1990, 8 (1), 1−15. (20) McLean, J. D.; Kilpatrick, P. K. Comparison of Precipitation and Extrography in the Fractionation of Crude Oil Residua. Energy Fuels 1997, 11, 570−585. (21) Li, Y.; Deng, X.; Yu, W. Group-type analyses of heavy petroleum fractions by preparative liquid chromatography and synchronous fluorescence spectrometry: analyses of aromatics by ring number of Liaohe vacuum gas oil, coker gas oil and heavy cycle oil. Fuel 1998, 77, 277−284. (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

CONCLUSION In this study, a preparatory-scale oil fractionation method was developed. The developed method was used for fractionating an oil sample into five fractions, and the obtained fractions were completely characterized by TLC−FID, FD and (+) APPI FT-ICR MS, and GC−AED. TLC−FID was employed for comparing the fractionation method by the conventional SARA method. FD−MS was employed for studying the HC class in the saturate and aro1 fractions, while (+) APPI FT-ICR MS was employed for studying the HC class in other fractions and especially heteroatom species. HR-MS data showed that the current fractionation method is effective for isolating basic and non-basic nitrogen, aromatic and non-aromatic sulfur, and nickel porphyrin compounds on a preparative scale. We believe that the current preparative fractionation method can be effectively used for isolating fractions on a larger scale, and the fractions thus obtained can be used to attain more molecularlevel information by various analytical techniques, such as tandem mass spectrometry and NMR.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.energyfuels.6b00296. Detailed HPLC flow program used to obtain the data shown in Figure 1 in the text (Table 1S), peak area of sulfur observed with the GC−AED chromatogram presented in Figure 6b (Table 2S), and flow chart showing the separation scheme used in this study (Figure 1S) (PDF)

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AUTHOR INFORMATION

Corresponding Author

*Telephone: 82-53-950-5333. Fax: 82-53-950-6330. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the Ministry of Knowledge Economy (MKE, Korea) and the Korea Science and Engineering Foundation (KOSEF) grants funded by the Korean government [Ministry of Education, Science and Technology (MEST)] (2015R1A2A1A15055585 and 2014R1A2A1A11049946) and the Industrial Strategic Technology Development Program (10038662, MALDI−TOF for the Diagnosis of BRCA Mutation and Genitourinary Infection Pathogen) funded by the Ministry of Trade, Industry and Energy, Republic of Korea.

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REFERENCES

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