Characterization of Nitrogen-Containing Compounds in Heavy Gas Oil

May 18, 2010 - These include gas chromatography coupled to mass spectrometry (GC/MS) ... Comprehensive two-dimensional GC (GC × GC) is a powerful ...
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Energy Fuels 2010, 24, 3572–3580 Published on Web 05/18/2010

: DOI:10.1021/ef1002364

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Characterization of Nitrogen-Containing Compounds in Heavy Gas Oil Petroleum Fractions Using Comprehensive Two-Dimensional Gas Chromatography Coupled to Time-of-Flight Mass Spectrometry Carin von M€ uhlen,† Eniz C. de Oliveira,‡ Claudia A. Zini,§ Elina B. Caram~ao,§ and Philip J. Marriott*,

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† Post-Graduation Program in Environmental Quality, Feevale University RS 239, 2755, CEP 93352-000, Novo Hamburgo, Rio Grande do Sul (RS), Brazil, ‡Post-Graduation Program in Environment and Development, UNIVATES, Lajeado, Rio Grande do Sul (RS), Brazil, §Chemistry Institute, Federal University of Rio Grande do Sul (UFRGS), Porto Alegre, Rio Grande do Sul (RS), Brazil, and Australian Centre for Research on Separation Science, School of Applied Sciences, RMIT University, GPO Box 2476, Melbourne 3001, Victoria, Australia.

Received March 2, 2010. Revised Manuscript Received May 5, 2010

Nitrogen (N)-containing compounds are naturally present in petroleum, and they are responsible for several deleterious effects that reduce the quality of products and negatively affect the processes involved in the upgrading of feedstock. The speciation of such compounds in petroleum heavy fractions is still a challenge. In the present work, N-containing compounds were characterized in heavy gas oil (HGO) fractions using a solid-liquid fractionation scheme and comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry. Classification and identification of compounds were carried out based on seven different categories of analytical information viz. retention times in first and second dimensions, analytical standards co-injection, the structured pattern of the separation space, the structured pattern of the separation space with the selection of specific m/z values, the library mass spectra match factor, and the characteristic deconvoluted mass spectra. All of these interpretations were available from a single analytical run followed by a standard injection. Compounds were extracted from the sample using an ion-exchange resin method to separate neutral and basic N-containing compounds, after a pre-fractionation step, using neutral aluminum oxide. This methodology allowed for the identification of 120 N-containing compounds and tentative identification of a further 108 compounds using their deconvoluted characteristic mass spectra as a basis for identification. Identified components included alkyl-indols, alkyl-carbazols, alkyl-benzocarbazols, alkyl-quinolines, alkyl-indene-pyridines, alkyl-benzoquinolines, and alkyl-dibenzoquinolines.

compounds be understood,6 as well as the mechanism of catalytic processes.7,8 The identification of N-containing compounds in petrochemical samples is a challenge because of the presence of multiple isomers, for a range of different compound classes, in a very complex mixture, with generally a relatively low concentration of the compounds. As an example, the total N content of about 90% of crude oils is less than 2%.9 Because heavy gas oil (HGO) is an intermediary fraction from vacuum distillation of the residue of the atmospheric distillation of crude oil,10 a higher concentration of heavy N-containing compounds is expected. A common approach for the analysis of N-containing compounds in several petrochemical samples is to increase the relative concentration and/or minimize the sample complexity, by fractionating N compounds into two different groups: neutral pyrrolic type and basic pyridinic type.11 The

Introduction Basic nitrogen (N)-containing compounds are responsible for poisoning of acidic sites in catalytic fluid processes and hydrocracking zeolite catalysts.1 The extent of poisoning is dependent upon the specific N compounds in the feedstock, and it is a function of their gas-phase basicity.2,3 Poisoning reduces the hydrotreating catalyst activity, thus restricting the ability to attain low-sulfur fuel specifications.4 Upon combustion, they form N-oxides (NOx), which contribute to engine corrosion and air pollution. Certain N compounds are responsible for fuel storage instability.5 These various consequences attributed to N-containing compounds in crude oils demand that detailed structure, reactivity, and origin of those *To whom correspondence should be addressed: Australian Centre for Research on Separation Science, School of Applied Sciences, RMIT University, GPO Box 2476, Melbourne 3001, Victoria, Australia. Telephone: þ61-3-9925-2632. Fax: þ61-3-9925-3747. E-mail: philip.marriott@rmit. edu.au. (1) Scherzer, J.; McArthur, D. P. Oil Gas J. 1986, 87, 76–82. (2) Fu, C. M.; Schaffer, A. M. Ind. Eng. Chem. Prod. Res. Dev. 1985, 24, 68–75. (3) Ho, T. C.; Katritzky, A. R.; Cato, S. J. Ind. Eng. Chem. Prod. Res. Dev. 1992, 31, 1589–1597. (4) Domı´ nguez-Crespo, M. A.; Dı´ az-Garcı´ a, L.; Arce-Estrada, E. M.; Torres-Huerta, A. M.; Cortez-De la Paz, M. T. Appl. Surf. Sci. 2006, 253 (3), 1205–1214. (5) Dorbon, M.; Bigeard, P. H.; Denis, J.; Bernasconi, C. Pet. Sci. Technol. 1992, 10, 1313–1341. r 2010 American Chemical Society

(6) Bennett, B.; Lager, A.; Russell, C. A.; Love, G. D.; Larter, S. R. Org. Geochem. 2004, 35 (11-12), 1427–1439. (7) Roussis, S. G.; Proulx, R. Energy Fuels 2004, 18 (3), 685–697. (8) Fu, J. M.; Klein, G. C.; Smith, D. F.; Kim, S.; Rodgers, R. P.; Hendrickson, C. L.; Marshall, A. G. Energy Fuels 2006, 20 (3), 1235– 1241. (9) Tissot, B. P.; Welte, D. H. Petroleum Formation and Occurrence; Springer: Berlin, Germany, 1984; p 699. (10) Hunt, J. M.; Philip, R. P.; Kvenvolden, K. A. Org. Geochem. 2002, 33, 1025–1052. (11) Richter, F. P.; Ceaser, P. D.; Meisel, S. L.; Offenhauer, R. D. Ind. Eng. Chem. 1952, 44, 2601–2605.

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GC  GC with nitrogen chemiluminescence detection (NCD) to separate N-containing compounds in diesel fuel, presenting the “roof-tile effect” for indoles, carbazole quinolines, and pyridines. Adam and co-workers32 showed quantitative studies on diesel samples and liquefied coal samples, using GCGCNCD for group-type analysis, and liquefied coal samples.15 In our previous study,33 quantitative analysis of N-containing compounds in HGO, using GC  GC-nitrogen phosphorus detector (NPD) and two different fractionation methods, was presented. N-Containing compounds equivalent to more than 2000 ppm total content of the oil were quantified, distributed in classes, such as indoles, alkyl carbazoles ranging from C0 to C6þ, alkyl benzocarbazoles ranging from C0 to C4þ, alkyl quinolines, and alkyl benzoquinolines. Several compounds were quantified for the first time in this kind of sample, with an acceptable structure of the separation space. However, it was not possible to identify unexpected compounds, although they were fully separated on the chromatogram. Adam and co-workers15 recently presented the application of GC  GC/ TOFMS for identification of N-containing compounds in diesel and liquefied diesel samples. Co-elution of different N-containing compound classes in the same region was observed; this prevents adequate identification when a N-selective detector is employed. Although the compounds identified in the study by Adam and co-workers presented a molecularmass range significantly lower than expected in HGO samples, the power of this analytical technique successfully demonstrated compound identification. Striebich and co-workers34 applied multi-dimensional GC/TOFMS to identify polar compounds in aviation fuels, reporting quantitative results for important polar classes, such as amines, indoles, pyridines, anilines, sulfur compounds, oxygenates, aromatics, and others. In the present study, analytical information provided by GC  GC/TOFMS analysis, such as retention times in first (1tR) and second (2tR) dimensions, co-injection of analytical standards, the structured pattern within the separation space in the total ion diagram (TID), the structured pattern within the separation space with selection of specific m/z values, the library mass spectral match factor, and/or the characteristic deconvoluted mass spectra, was used to identify higher molecularmass N-containing compounds in HGO samples.

neutral N species usually comprise pyrrole, indole, carbazole, and their higher alkylated and benzylated analogues. Basic N species usually include pyridines, quinolines, benzoquinolines, and their alkylated derivatives. Extraction and concentration of N compounds have been performed by either liquid/ liquid extraction (LLE)12 or solid-phase extraction (SPE),13,14 although the quantitative fractionation of neutral and basic N compounds is subject to continuing research.15 Several methods involving petroleum and petroleum product analysis of N-containing compounds have been developed using a variety of analytical techniques. These include gas chromatography coupled to mass spectrometry (GC/ MS),12,14 GC equipped with a pulsed flame photometric detector (GC-PFPD) and ammonia chemical ionization MS,16 particle beam liquid chromatography/MS (LC/MS),17-19 mass spectrometry with atmospheric pressure chemical ionization,20 positive-ion electrospray ionization MS (ESIþ),21 time-of-flight secondary ion MS (TOF SIMS)22 and electron ionization, field desorption ionization, and electrospray ionization Fourier transform ion cyclotron resonance MS (FT-ICR MS).8 Although several fractionation steps and the most powerful analytical instrumentation may be employed, it is still not possible to speciate (separate) all N-containing compounds in petroleum samples. Comprehensive two-dimensional GC (GCGC) is a powerful analytical technique that has been applied to petrochemical samples since its inception,23-27 and this persists as one of the key GC  GC applications. GC  GC offers much more informing power and separation power than conventional GC separations.28,29 The presence of ordered structures in 2D separation space30 is a unique attribute of GCGC that often allows for unequivocal chemical compound classification and identification through a visual inspection of the contour plots. Wang and co-workers31 demonstrated the capability of (12) Pasquale, A. J.; Bauserman, J. M.; Mushrush, G. W. Pet. Sci. Technol. 2009, 27 (18), 2192–2199. (13) da Luz, E. R.; Gonsalves, T. F. M.; Aucelio, R. Q. J. Sep. Sci. 2009, 32 (12), 2058–2065. (14) Oliveira, E. C.; Campos, M. C. V.; Lopes, A. S.; Vale, M. G. R.; Caram~ ao, E. B. C. J. Chromatogr., A 2004, 1027, 171–176. (15) Adam, F.; Bertoncini, F.; Dartiguelongue, C.; Marchand, K.; Thiebaut, D.; Hennion, M. C. Fuel 2009, 88, 938–946. (16) Shi, Q.; Xu, C. M.; Zhao, S. Q.; Chung, K. H. Energy Fuels 2009, 23, 6062–6069. (17) Mao, J.; Pacheco, C. R.; Traficante, D. D.; Rosen, W. J. Chromatogr., A 1994, 684 (1), 103–111. (18) Mao, J.; Pacheco, C. R.; Traficante, D. D.; Rosen, W. Fuel 1995, 74 (6), 880–887. (19) Mao, J.; Pacheco, C. R.; Traficante, D. D.; Rosen, W. J. Liq. Chromatogr. 1995, 18 (5), 903–916. (20) Cheng, X.; Zhao, T.; Fu, X.; Hu, Z. Fuel Process. Technol. 2004, 85 (13), 1463–1472. (21) Qian, K.; Edwards, K. E.; Diehl, J. H.; Green, L. A. Energy Fuels 2004, 18 (6), 1784–1791. (22) Toporski, J.; Steele, A. Org. Geochem. 2004, 35 (7), 793–811. (23) Blomberg, J.; Schoenmakers, P. J.; Beens, J.; Tijssen, R. J. High Resolut. Chromatogr. 1997, 20 (10), 539–544. (24) Vendeuvre, C.; Ruiz-Guerrero, R.; Bertoncini, F.; Duval, L.; Thiebaut, D. Oil Gas Sci. Technol. 2007, 62 (1), 43–55. (25) Venkatramani, C. J.; Phillips, J. B. J. Microcolumn Sep. 1993, 5 (6), 511–516. (26) von M€ uhlen, C.; Zini, C. A.; Caram~ao, E. B.; Marriott, P. J. Quim. Nova 2006, 29 (4), 765–775. (27) von M€ uhlen, C.; Zini, C. A.; Caram~ao, E. B.; Marriott, P. J. J. Chromatogr., A 2006, 1105, 39–50. (28) Kidwell, D. A.; Riggs, L. A. Forensic Sci. Int. 2004, 145 (2-3), 85–96. (29) Marriott, P. J.; Morrison, P. D.; Shellie, R.; Dunn, M. S.; Sari, E.; Ryan, D. LCGC Europe 2003, 16 (12A), 23–31. (30) Marriott, P. J.; Massil, T.; H€ ugel, H. J. Sep. Sci. 2004, 27, 1273– 1284. (31) Wang, F. C. Y.; Robbins, W. K.; Greaney, M. A. J. Sep. Sci. 2004, 27 (5-6), 468–472.

Experimental Section Samples and Chemicals. Indole, carbazole, quinoline, iso-quinoline, 5,6-benzoquinoline, 7,8-benzoquinoline, and 7-H-dibenzo-c, g-carbazole standards were purchased from AccuStandard, Inc. (New Haven, CT). Dichloromethane (analytical grade) supplied from Merck (Kilsyth, Victoria, Australia) was used to prepare the standard solutions and for sample dilution. The HGO residue was produced by Petrobras, in Brazil. This sample presented a total acidity number of 0.15 mg of KOH g-1. A prefractionation step was performed using a neutral aluminum oxide chromatographic column (CC) providing separation of compounds in the following groups: hydrocarbons, resins (compounds of low molecular mass and intermediate polarity), and asphalthenes (polar compounds with high molecular mass). These fractions were eluted using hexane (F1), n-hexane/ dichloromethane (F2), dichloromethane (F3), and methanol (F4) in triplicate. Resins (F3) were further fractionated using (32) Adam, F.; Bertoncini, F.; Brodusch, N.; Durand, E.; Thiebaut, D.; Espinat, D.; Hennion, M. C. J. Chromatogr., A 2007, 1148 (1), 55–64. (33) von M€ uhlen, C.; Oliveira, E. C.; Morrison, P. D.; Zini, C. A.; Caram~ao, E. B.; Marriott, P. J. J. Sep. Sci. 2007, 30, 3223–3232. (34) Striebich, R. C.; Contreras, J.; Balster, L. M.; West, Z.; Shafer, L. M.; Zabarnick, S. Energy Fuels 2009, 23, 5474–5482.

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Figure 1. TID obtained with GC  GC/TOFMS from a neutral fraction of a HGO sample: (A) without classification and (B) with classification regions presented. In panel B, IC stands for alkyl-indoles (I) from C0 to C3 on the upper left part of the TID, CC located at the lower region of the TID corresponds to alkyl-carbazoles from C0 to C12, and in the upper part of the TID, BC C corresponds to alkyl-benzocarbazoles from C0 to C6.

Figure 2. Total ion chromatogram (TIC) and selected ions used to demonstrate MS deconvolution of peaks: 583-2, second modulated peak of tetramethylphenanthrene; 580-B, base modulation of pentamethylcarbazole; 584-1 and 581-B, modulated non-identified peaks.

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ion-exchange resins (Amberlyst A-27 and A-15), providing basic and neutral compound separation, also in triplicate. This fractionation procedure was previously described.14 GC  GC/TOFMS System. The GC  GC system comprised a 6890 GC (Agilent Technologies, Burwood, Australia), retrofitted with an Everest model longitudinally modulated cryogenic system (LMCS, Chromatography Concepts, Doncaster, Australia), coupled to a TOFMS from LECO, Model Pegasus II. The instrument was equipped with a model 6873 auto-sampler and ChromaTOF 2.2 software. The column set used consists of a nonpolar first dimension (1D) capillary column BPX5 phase (5% phenyl polysilphenylenesiloxane) with dimensions of 30 m length  0.25 mm inner diameter  0.50 μm film thickness (df) serially coupled with a polar second dimension (2D) capillary column BPX50 phase (50% phenyl polysilphenylene-siloxane) with dimensions of 1.0 m length0.15 mm inner diameter0.15 μm df. Both columns were from SGE International (Ringwood, Australia). A transfer line with dimensions of 0.5 m0.10 mm inner diameter was used to couple the second-dimension column to the TOFMS. A conventional split/splitless injector was used at 300 °C, with an injection volume of 2.0 μL in pulse splitless mode, with a split flow of 50 mL min-1 1 min after injection and 20 mL min-1 2 min after injection. Oven temperature program conditions were as follows: initial temperature of 60 °C for 0.2 min, programmed at 20 °C min-1 until 170 °C (hold for 5 min), and then 2 °C min-1 to 290 °C (hold for 20 min). A constant helium carrier gas flow of 1.0 mL min-1 was applied throughout the whole analysis after pulse splitless injection (flow of 51 mL min-1 for 1 min). The MS transfer line temperature was 350 °C, and the ion source temperature was 200 °C. Data were collected over a mass range of 45415 units at a data acquisition rate of 100 Hz. The detector voltage was -1.90 kV, and 70 eV was employed for electron ionization. The thermostatically controlled cryogenic trap was maintained at about 40 °C from 4 min to the end of the run, and the modulation period was 6 s, commencing at 4 min to the end of the run. Data Handling. Identification of N-containing compounds in basic and neutral fractions of HGO samples was carried out based on seven categories of analytical information, when available: retention times in first (1tR) and second (2tR) dimensions, co-injection of analytical standards, the structured pattern of the separation space in the TID, the structured pattern of the separation space observed when specific m/z values were selected [defined as the selected ion diagram (SID)], the library mass spectral match factor, and/or the characteristic deconvoluted mass spectra alone. The latter spectral data were interpreted on the basis of first principles because several compounds (especially isomers) are not listed in the National Institute of Standards and Technology (NIST) library used (version 2). For data processing, ChromaTOF software, version 3.25, was used.

Results and Discussion

Figure 3. SID obtained with GC  GC/TOFMS for a neutral fraction of a HGO sample. (A) IC represents alkyl-indoles from C0 to C3. (B) CC at the lower region of the TID corresponds to alkylcarbazoles from C0 to C12. (C) BC C corresponds to alkyl-benzocarbazoles from C0 to C6. Selected ions are presented in Table 1.

Fractionation of HGO Samples. The recovery (m/m) of the separate HGO fractions were F1, 35 ( 4.9%; F2, 26 ( 0.15%; F3, 4.2 ( 0.52%; and F4, 7.4 ( 0.12%. The largest fraction of compounds in HGO consists of saturated and aromatic hydrocarbons (F1 þ F2, 61%). N-Containing compounds were concentrated in the resin fraction (F3), and it was further separated into neutral and basic fractions, which was found to be important to allow for the identification of compounds even with the use of GC  GC/TOFMS. A separate study was performed without fractionation of the sample (results not shown), and it was not possible to identify most of the N-containing compounds presented here. On the other hand, direct identification of those compounds in a pure sample (without fractionation) may be possible if a higher concentration of N-containing compounds is present, although trace level components will still be difficult.

Column Set. A 1D BPX5 column and a 2D BPX50 column were employed, which is a commonly used set for petrochemical samples.27,31 Adam and co-workers15,32 used cyanopropyl (CNP) and polyethylene glycol (PEG) columns for the 2 D phase to improve the separation of neutral and basic N-containing compounds. This type of column can be useful to achieve a better separation for low-molecular-weight polar compounds in 2D, such as anilines, quinolines, and indols. On the other hand, the relatively low upper temperature limit of the CNP and PEG columns limits the separation to low-molar-mass compounds, because their maximum temperatures are around 250 and 280 °C, respectively, compared to 360 °C or higher for a 50% phenyl column. Thus, these polar 2D CNP and PEG phase columns cannot be applied for HGO analysis, because a higher boiling point range is required for the N-containing compounds of this HGO fraction. 3575

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Table 1. Selected m/z Values, Characteristic of N-Containing Compounds compounds typical neutral fraction alkyl-indoles C0 C1 C2 C3 C4 C5 alkyl-carbazoles C0 C1 C2 C3 C4 C5 C6 C7 C8 C9 C10

m/z

117 131 145 159 173 187 167 181 195 209 223 237 251 265 279 293 307

compounds C11 C12 C13 alkyl-benzocarbazoles C0 C1 C2 C3 C4 C5 C6 typical basic fraction alkyl-quinolines C0 C1 C2 C3 C4 C5 C6

Identification of Compounds in the Neutral Fraction. A TID experimentally obtained for a neutral fraction of HGO is illustrated in Figure 1A. Automated integration with spectral deconvolution of this chromatogram resulted in more than 10 000 compounds in the peak table. Alkyl-carbazoles and alkyl-benzocarbazoles were expected in the central region of the TID, similar to the findings in our previous work using GC  GC-NPD33 for the same sample under similar conditions. In addition to the presence of N-containing compounds, this region also includes polyaromatic hydrocarbons (PAHs) and other compounds, such as saturated hydrocarbons, which may not be expected in this fraction of HGO, because of presumably incomplete elution of hydrocarbons in the previous fractionation step. PAHs are detected by TOFMS but not by the NPD used previously. PAHs exhibit wrap-around in the color plot, and saturated hydrocarbons are present in this extract but in low concentrations, as illustrated in Figure 1A. It is important to point out that most of those compounds were removed in fractions 1 and 2 (61% of the sample), but they are still present in fraction 3, because of the high complexity of the sample. Because the resolution of those compounds was not the aim of the present work, the presence of this wrap-around effect was not considered a problem. With the focus on selected ions from processed data, all efforts in the method optimization were applied to chromatographically resolve N-containing compounds as completely as possible, maintaining the roof-tile structure for those compounds, as can be observed in Figure 1B and Figure 2. Even with the best chromatographic resolution possible, the alkyl-carbazole region still coelutes with PAHs and other compounds. Several of those compounds were resolved just by mass spectra deconvolution, such as pentamethylcarbazole, illustrated in Figure 2. Each vertical line in Figure 2 represents a deconvoluted peak with S/N higher than 10, which means that four peaks were deconvoluted with the same 2D retention time (1tR, in s), in a 0.9 s 2tR window. The PAH eluting just before pentamethylcarbazole presented the same 237 and 222 masses as pentamethylcarbazole. Thus, deconvolution will not be possible with a quadrupole MS (even with GCGC operation), because of the peak skewing of mass spectra over the peak and the lower acquisition rate. Because mass spectral fragmentation patterns of aromatic N-containing compounds are very unique and easily recognized, their identification may be performed using MS library

m/z

compounds

321 335 349

alkyl-indene-pyridines C0 C1 alkyl-benzoquinolines C0 C1 C2 C3 C4 C5 C6 alkyl-dibenzoquinolines C0 C1 C2 C3 C4 C5

217 231 245 259 273 287 301 129 143 157 171 185 199 213

m/z 167 181 179 193 207 221 235 249 263 229 243 257 271 285 299

searching of deconvoluted peaks for isomer classification; however, specific isomer structural assignment is not available in the absence of authentic standards. The generic molecular structure of these compounds and characteristic ions were investigated and presented in previous work using GC/MS for standard compounds14 and are in agreement with the patterns found in TOFMS mass spectra of the HGO sample. Molecular ions from the selected spectra were used to identify class patterns in the separation space using SIDs. These diagrams were used as basic information to construct a classification system superimposed on the GC  GC diagram, using the classification tool provided with ChromaTOF software. All selected regions are presented in Figure 1B. Figure 3 shows an expansion of the respective classification regions. The selected ions are listed in Table 1. Note that, from among this list of N-compound molecular ions, only the C0 and C1 alkylcarbazoles and alkyl-indene-pyridines have equivalent ions of m/z 167 and 181 but there is no coincidence of these compounds in 2D space (see later); hence, their unique analysis is straightforward. The selected ions were also found in non-N-containing compounds outside the classification regions, as presented in Figure 3. It illustrates that a single ion monitoring (SIM) approach, using 1D GC/MS is not sufficient to isolate such compounds, in this particular sample, and that the 2D positions in combination with the TID have more diagnostic information. In addition, several peaks were detected inside a classification region and presented characteristic mass spectra expected for the selected class, but they were not automatically identified in the peak table. Because the number of compounds (especially for isomers and homologues) from each class in the MS library is limited, several compounds were accompanied by low match values following the MS library search, although the limited number of similar mass spectra in the library resulted in high probability (P) values. As an example, just one reference spectrum for C5 benzocarbazoles (pentamethylcarbazole) was available in the MS library, and at least six compounds were detected with a similar mass spectrum, in the same region of the separation space. For benzocarbazole, there were four characteristic spectra in the MS library, but none for other alkyl derivatives of that class. A total of 50 compounds were identified by the NIST library as N-containing compounds with similarity values (S) higher than 800. These compounds are listed in Table 2. 3576

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Table 2. Compounds Identified in the Neutral Fraction of HGO Samples Based on the Structured Pattern within the Separation Space and MS Library Match number

1

2

tR (s)

name

S

R

P

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34

558 636 666 678 756 780 810 816 924 942 984 1638 1806 1908 1920 1938 1956 1980 2070 2076 2100 2118 2130 2148 2178 2196 2202 2226 2226 2238 2256 2286 2292 2316

3.67 4.25 4.36 4.46 4.66 4.88 4.89 5.02 5.18 5.21 5.42 2.19 1.97 2.17 2.15 1.48 2.64 1.84 1.89 2.00 1.84 2.20 2.68 2.20 2.12 2.42 2.02 1.74 2.42 2.39 1.56 2.32 1.95 1.95

869 905 935 913 894 939 888 911 905 884 917 924 937 930 931 932 929 915 938 939 935 945 840 916 919 943 931 823 946 937 910 910 856 826

869 910 940 913 894 939 888 911 905 906 917 924 941 935 935 939 934 932 941 937 942 945 856 939 922 949 937 823 946 943 928 914 867 826

5349 2188 4968 3656 1333 4251 1053 2221 3470 5876 4221 2203 3710 3327 3080 2269 3701 6839 2523 2311 1966 2489 4187 8784 2854 2511 1749 6129 2829 2692 1997 2958 4233 5273

35 36 37 38 39 40 41

2322 2340 2352 2358 2400 2442 2466

1.71 1.85 1.82 2.10 2.03 2.00 2.37

923 915 923 926 921 866 848

932 915 933 935 927 891 866

1959 1937 1865 1976 2296 3477 7605

42 43 44 45 46 47 48 49 50

2484 2508 2748 2844 2928 3204 3366 3516 3894

2.35 2.39 1.83 0.18 3.49 4.07 4.99 4.39 5.68

indolea methylindole methylindole methylindole dimethylindole dimethylindole dimethylindole dimethylindole trimethylindole trimethylindole trimethylindole carbazolea methylcarbazole methylcarbazole methylcarbazole dimethylcarbazole methylcarbazole ethylcarbazole dimethylcarbazole dimethylcarbazole dimethylcarbazole dimethylcarbazole ethylcarbazole ethylcarbazole dimethylcarbazole dimethylcarbazole dimethylcarbazole trimethylcarbazole dimethylcarbazole dimethylcarbazole trimethylcarbazole dimethylcarbazole trimethylcarbazole dihydro-dimethylbenzoquinoline trimethylcarbazole trimethylcarbazole trimethylcarbazole trimethylcarbazole trimethylcarbazole trimethylcarbazole dihydro-dimethylbenzoquinoline trimethylcarbazole trimethylcarbazole pentamethylcarbazole octadecenamide dimethylphenylindole benzocarbazole benzocarbazole diphenylpyridine butylmethylphenylimidazolidinone

921 922 805 842 819 881 852 823 899

934 926 805 842 819 937 895 935 962

4010 2393 7099 4757 4450 6267 3059 6979 5973

a

tR (s)

Table 3. Compounds Tentatively Identified in the Neutral Fraction of HGO Samples Based on the Structured Pattern within the Separation Space and Mass Spectra Profile carbazoles number 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38

1

tR (s)

C4 2364 2412 2466 2580 2604 2634 2658 2712 2718 2760 2772 2832 C5 2580 2604 2676 2808 2982 3084 C6 2730 2766 2772 2808 2886 2898 2928 2958 3006 3012 3132 3150 3228 3300 C7 2994 3008 3216 C8 3360 3396 3450

benzocarbazoles 2

tR (s)

1.280 1.67 1.40 1.66 1.70 1.76 1.86 1.96 2.22 2.09 2.09 2.17 1.30 1.12 1.37 1.72 1.86 2.15 0.98 1.11 0.99 1.22 1.53 1.19 1.37 1.37 1.48 1.54 1.80 1.65 1.84 1.92 1.00 1.19 1.39 1.20 1.35 1.34

number 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81

1

tR (s)

C1 3372 3450 3468 3504 3516 3588 3624 3696 C2 3480 3540 3612 3654 3666 3702 3708 3732 3762 3822 3834 3858 3924 C3 3798 3852 3864 3906 3936 4008 4020 4028 4074 C4 3972 4020 4044 4062 4086 4104 4158 4182 4200 4236 4248 4284 C5 4248

2

tR (s)

3.73 3.86 3.710 4.07 4.39 4.55 4.51 4.97 3.16 3.17 3.40 3.43 3.7 3.43 4.00 4.02 3.94 4.10 4.44 4.29 4.33 3.17 3.19 3.34 3.54 3.41 3.52 3.58 3.61 3.84 2.88 2.80 2.93 2.96 2.16 3.17 3.20 3.15 3.32 3.36 3.46 3.73 2.96

identified on the basis of only deconvoluted mass spectral profiles, retention times in both dimensions, and information taken from SID structured elution patterns. These compounds are listed in Table 3. The roof-tile effect of the alkyl-indole region (a relationship that presents homologues and isomers of compounds in a structured pattern that resembles a roof-tile effect in the 2D space) was not characterized when the GC  GC-NPD33 was used, but the use of MS information from GC  GC/ TOFMS resulted in a well-characterized structured alkylindole region, as demonstrated by its classification region in Figure 3. Some compounds identified in Table 2, such as dihydrodimethylbenzoquinoline and octadecenamide, were expected in the basic fraction and not in the neutral fraction. This information is consistent with the low extraction efficiency toward molecular class differentiation observed using different extraction techniques.15

Confirmation with pure analytical standard co-injection.

The structure of carbazole allows four possible methyl isomers, and all of them were easily detected, as illustrated in Figure 3B and Table 2. For ethyl carbazoles, only three of four isomers were detected, while the other CC2 compounds were dimethyl carbazole isomers. It is possible that other isomers were not present in the sample because of a specific biosynthesis process or chemical reaction.35 The structured separation of those compounds by GC  GC and identification by TOFMS will permit a detailed study on the origin of this distribution. Another 81 compounds were tentatively (35) Dorbon, M.; Schmitter, J. M.; Garrigues, P.; Ignatiadis, I.; Ewald, M.; Arpino, P.; Guiochon, G. Org. Geochem. 1984, 7 (2), 111– 120.

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von M€uhlen et al.

Figure 4. TID obtained with GC  GC/TOFMS from a basic fraction of a HGO sample: (A) before and (B) after classification process. In panel B, Q represents alkyl-quinolines from C2 to C3 on the upper left part of the TID, on the lower region of the TID, B corresponds to alkyl-benzoquinolines from C0 to C5 and IP corresponds to indene-pyridines from C0 to C1, respectively, and DBQ corresponds to alkyl-dibenzoquinolines from C0 to C5 to the right part of the TID.

Identification of Compounds in the Basic Fraction. A typical GCGC/TOFMS TID for the basic fraction is presented in Figure 4A. The presence of a PAH region in this fraction was not as abundant as in the neutral fraction, suggesting a more selective extraction toward PAH in the neutral fraction. The same classification procedure adopted for compounds in the neutral fraction was adapted to the basic fraction, using the typical m/z values observed for basic compounds, as listed in Table 1. All classification regions selected are illustrated in Figure 4B. The roof-tile effect observed for alkyl-quinolines, indenepyridines, alkyl-benzoquinolines, and alkyl-dibenzoquinolines for selected ions is presented in Figure 5. Although the number of coeluting/overlapping regions for successive homologues was not very extensive, identifying the region of alkyl-quinolines was more challenging than for the other regions, because for some peaks, the mass spectra did not follow the characteristic expected pattern. It means that, even when using GC  GC coupled with MS, if a SIM mode were employed (e.g., with a quadrupole MS system) or if the mass spectra were not correctly deconvoluted, a misclassification might occur. The use of selective detectors to quantify N-containing compounds of the basic fraction based on chemical class distribution in the separation space would result in overquantification, in the case of having interfering compounds in the same region. However, the use of a TOFMS detector should facilitate correct quantification of the required chemical class.

Figure 5. SID obtained with GC  GC/TOFMS from a basic fraction of a HGO sample. (A) Q represents alkyl-quinolines. (B) B corresponds to alkyl-benzoquinolines from C0 to C5 and IP corresponds to indene-pyridines from C0 to C1, respectively. (C) DBQ corresponds to alkyl-dibenzoquinolines from C0 to C5 to the right section of the TID.

Compounds of the basic fraction identified through a comparison of experimental MS and commercial library MS, also taking into consideration the molecular information from the structured pattern of the separation space, are presented in Table 4. A total of 90 N-containing compounds were identified using the formerly explained criteria, and another 27 compounds were tentatively identified in that sample based on only deconvoluted MS evaluation (Table 5). From the 90 compounds identified, 40% were alkyl-carbazoles or alkyl-indoles, which would be expected in the neutral fraction. Most of these compounds were observed in both fractions, but alkyl-benzocarbazoles were concentrated in the basic fraction and not in the neutral fraction. This demonstrates that the employed neutral and basic separation methodology was not completely selective. These findings were not so evident using only 1D GC/MS 3578

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: DOI:10.1021/ef1002364

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Table 4. Compounds Identified in the Basic Fraction of HGO Samples Based on the Structured Pattern within the Separation Space and MS Library Match number 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72

1

tR (s)

750 930 942 1158 1290 1458 1524 1554 1560 1584 1614 1644 1662 1686 1704 1710 1734 1776 1800 1818 1848 1866 1872 1884 1902 1914 1920 1926 1926 1944 1956 1962 1974 1986 1998 2010 2022 2058 2058 2070 2082 2094 2100 2130 2130 2142 2154 2184 2202 2208 2208 2214 2232 2244 2250 2262 2262 2328 2340 2340 2358 2406 2424 2460 2466 2466 2466 2472 2478 2490 2508 2514

2

tR (s)

name

S

R

P

4.42 4.94 4.97 0.39 0.39 0.89 1.47 1.49 1.91 0.78 1.78 2.17 1.22 1.92 1.15 1.96 1.99 1.64 1.70 1.60 3.32 1.68 1.83 1.75 1.87 2.17 1.75 1.25 2.14 1.45 1.32 2.59 2.19 1.84 2.30 1.44 1.61 1.59 2.08 1.94 1.95 2.02 1.79 1.89 2.22 2.34 2.20 0.89 2.38 2.01 2.49 1.39 2.36 2.35 1.29 1.58 2.75 1.68 1.85 2.93 1.75 1.96 3.15 3.21 2.11 2.17 3.37 3.49 2.01 2.34 2.14 2.34

dimethylquinoline trimethylquinoline trimethylquinoline indenepyridine methylindenepyridine methylindenepyridine 7,8-benzoquinolinea benzoquinoline phenanthroline dimethylcarbazole 5,6-benzoquinolinea carbazolea methylbenzoquinoline benzoquinoline methylbenzoquinoline benzoquinoline benzoisoquinoline methylbenzoquinoline methylbenzoquinoline methylbenzoquinoline indenopyridinone methylbenzoquinoline methylbenzoquinoline methylbenzoquinoline methylbenzoquinoline methylcarbazole methylbenzoquinoline dimethylbenzoquinoline methylcarbazole dimethylcarbazole dimethylbenzoquinoline methylcarbazole methylbenzoquinoline ethylcarbazole methylbenzoquinoline dimethylbenzoquinoline dimethylbenzoquinoline dimethylbenzoquinoline phenylisoquinoline dimethylcarbazole dimethylcarbazole phenylisoquinoline dimethylcarbazole methylphenylindole dimethylcarbazole phenylisoquinoline ethylcarbazole trimethylbenzoquinoline dimethylcarbazole dimethylcarbazole phenylisoquinoline trimethylcarbazole dimethylcarbazole dimethylcarbazole trimethylbenzoquinoline trimethylcarbazole indeneisoquinoline trimethylcarbazole trimethylcarbazole indeneisoquinoline trimethylcarbazole trimethylcarbazole phenylisoquinoline indeneisoquinoline trimethylcarbazole trimethylcarbazole dibenzoquinoline dibenzoquinoline trimethylcarbazole trimethylcarbazole trimethylcarbazole trimethylcarbazole

902 902 892 918 840 839 961 964 849 838 933 899 878 909 895 901 862 851 863 871 805 914 829 800 876 854 869 827 861 904 832 913 824 811 813 810 887 849 877 903 896 806 903 834 917 820 826 819 877 824 802 877 914 917 811 856 923 878 883 906 892 857 801 859 860 800 929 900 869 882 818 858

921 902 892 918 848 870 965 969 886 849 939 919 886 910 904 903 880 858 873 880 817 924 850 800 884 871 879 840 884 922 834 914 828 861 813 835 887 859 896 915 913 825 925 844 929 878 872 820 885 858 835 886 919 925 811 864 923 900 889 906 904 864 882 890 870 848 929 900 885 905 840 874

7344 6874 5002 7181 5340 6187 7648 6501 6690 1974 4199 4127 6300 3734 6284 5164 2300 4816 6722 6461 9014 7524 5354 6363 5173 2848 5945 5812 3111 2071 5306 4593 3439 4406 3942 6416 7730 7282 4965 2385 2067 2237 1785 6609 1709 2089 6947 3701 1743 1449 4348 2606 2592 1874 3891 1922 3653 1548 2051 3565 1729 1935 8481 4929 2210 2011 6739 3244 2265 3671 1645 1710

Table 4. Continued number 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 a

1

tR (s)

2

2556 2646 2658 2670 2718 2772 2796 2814 2868 3054 3162 3180 3198 3276 3300 3312 3630 4602

tR (s)

name

S

R

P

3.53 2.93 3.10 3.29 3.07 3.16 3.44 3.25 3.42 3.49 3.68 3.90 3.79 3.91 3.90 4.21 3.51 2.25

dibenzoquinoline benzocarbazole benzocarbazole benzocarbazole benzocarbazole benzocarbazole benzocarbazole indenequinoline benzocarbazole dibenzoquinoline dibenzoquinoline dibenzoquinoline dibenzoquinoline dibenzoquinoline dibenzoquinoline dibenzoquinoline dimethylindenoquinoline tribenzoquinoline

864 823 878 821 839 830 843 831 819 862 915 818 874 867 883 840 803 911

864 846 884 841 846 898 854 880 849 883 936 851 895 899 906 886 822 937

3366 3648 4536 4253 5217 2916 4482 3798 4056 7802 9797 9230 7796 9704 9666 9611 8223 5976

Confirmation with pure analytical standard co-injection.

Table 5. Compounds Tentatively Identified in the Basic Fraction of HGO Samples Based on Structured Pattern within the Separation Space and Mass Spectra benzoquinolines number 1 2 3 4 5 6 7 8

1

tR (s)

C3 2136 2160 C4 2382 2412 2460 C5 2598 2694 2862

dibenzoquinolines 2

tR (s) 0.84 1.40 0.77 0.77 0.82 0.72 0.77 1.19

number 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27

1

tR (s)

C1 3198 3342 3390 3408 C2 3492 3522 3588 3636 3642 3684 C3 3744 3870 3900 3966 C4 3848 4050 4104 4140 4230

2

tR (s) 2.83 3.51 3.33 3.50 2.73 2.89 3.40 2.99 3.33 3.49 2.48 3.22 3.13 3.22 2.28 2.56 2.89 2.83 3.17

analysis, for the same kind of sample.14 The development of quantitative and fully selective fractionation and extraction techniques are still a challenge for N-containing compounds in petrochemical samples. However, the use of GC  GC/ TOFMS technology significantly aids the unique identification of all respective compound classes in the sample. A newer version of the ChromaTOF software also allows for the classification of compounds based on the presence of a heteroatom among identified compounds in the peak table, such as nitrogen. This tool can reduce the time spent in searching for N-containing compounds in a peak table with more than 10 000 peaks, which is an important advance for simplification of target compound class identification and is recommended for such work in the future. Conclusions Speciation of N-containing compounds in an HGO sample using GC  GC/TOFMS and based on a separation strategy 3579

Energy Fuels 2010, 24, 3572–3580

: DOI:10.1021/ef1002364 1

von M€uhlen et al. 2

that incorporated a nonpolar D column phase and D polar phase has been accomplished. In comparison to previous GC GC-NPD studies, MS provides additional scope for molecular identification, the use of additional analytical information provided by GCGC/TOFMS over and above retention times in 1D and 2D, and analytical standard co-injection, including improved structured elution patterns in the separation space in the TID, the structured pattern in the separation space with selection of specific m/z values, library MS match factor, and characteristic deconvoluted mass spectra. Collectively, these were a key strategy to achieve successful identification after the fractionation and separation steps. It was possible to identify or tentatively identify 228 N-containing compounds in a HGO sample. Almost half of these components (108 compounds) were not present in the commercial

mass spectra library; however, on the basis of the abovementioned information, tentative identification of these compounds was feasible, although it was not possible to precisely confirm their isomeric structures. With regard to 2D columns, comparative selectivity provided by a new generation of high-temperature polar phases would be interesting to study. Acknowledgment. Carin von M€ uhlen thanks the Conselho Nacional de Desenvolvimento Cientı´ fico e Tecnol ogico (CNPq), a Brazilian governmental institution, that promotes scientific and technological development and the Coordenac-~ ao de Aperfeic- oamento de Pessoal de Nı´ vel Superior (CAPES) for Ph.D. grants. The authors thank Petrobras for kindly providing the HGO samples. The technical assistance of Mr. Paul Morrison is gratefully acknowledged.

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