Energy Fuels 2009, 23, 5003–5011 Published on Web 08/25/2009
: DOI:10.1021/ef900289s
Discriminatory Analysis of Crude Oils Using Biomarkers Masato Taki,*,† Teruyuki Asahara,† Yasushi Mandai,† Toshiaki Uno,† and Masatoshi Nagai‡ †
Coast Guard Research Center, Japan Coast Guard, 1156, Tachikawa-city, Tokyo 190-0015, Japan, and ‡Graduate School of Bio-applications and Systems Engineering, Tokyo University of Agriculture and Technology, 2-24, Nakamachi, Koganei-shi, Tokyo 184-8588, Japan Received April 3, 2009. Revised Manuscript Received July 22, 2009
Forty-one types of crude oils were divided into the following six groups, based on the analysis of the homologous series of hopanes of 18R-22,29,30-trisnorneohopane (1), 17R-22,29,30-trisnorhopane (2), 17R-21β(H)-norhopane (3), oleananes (4), and 17R-21β(H)-hopane (5) as biomarkers by GC-MASS, in combination with the inductively coupled plasma-atomic emission spectroscopy (ICP-AES) measurement of nickel and vanadium and X-ray fluorescence spectroscopy (XFS) of sulfur: (a) northern Middle East; (b) eastern Middle East; (c) southern Middle East; (d) Borneo Island, Malaysia, and Vietnam; (e) Sumatra Island, China, Gabon, and Russia; and (f) Mexico crude oils. The relationship between the ratios of 4/5 and 3/5 classified the 41 crude oils into three groups of (d), (e), and (a-c) and (f), which was divided into (a) and (f), (b), and (c), based on the 3/5 and 1/2 ratios. Furthermore, the distribution of vanadium and nickel showed that the Middle East crude oils were subdivided into two groups: the southern parts and the northern parts. The individual Mexican crude oil was differentiated by the determination of the sulfur content of all the crude oils in combination with the vanadium and nickel contents. The crude oils were discriminated based on the hopane analysis in combination with the ICP-AES analysis of nickel and vanadium and XFS of sulfur. This combination method is superior for the identification of crude oils. Two analytical cases of spilled oils and heavy oils provided the discrimination into the individual oils based on the analysis of the hopane series.
Spilled oils and drifted ashore oils can be analyzed based on the distribution of the hopanes.4-8 The spilled oils have been traditionally analyzed for their composition of alkanes or polycyclic aromatic compounds by gas chromatographyflame ionization detection (GC-FID) spectrometry and gas chromatography-mass spectrometry (GC-MS).4 However, the spilled oils are affected by evaporation and chemical decomposition and are then often not distinguishable. Furthermore, the crude oils contain inorganic compounds or metals in a ppb or ppm concentration (e.g., relatively measurable quantities of vanadium, nickel, and sulfur). Nickel and vanadium in coordinated forms with porphyrins are present, along with the major metals in petroleum.1,2,9 The analysis of nickel and vanadium has been reported by several researchers.9-11 However, the nickel and vanadium analysis has not been available for traditional biomarkers, such as the hopanes. In this study, the crude oils and spilled oils were identified by the determination of the hopane series in combination with the nickel and vanadium analyses. Forty-one crude oils imported into Japan and spilled heavy oils were differentiated by the analytical methods for the hopane series by GC-MS, in combination with nickel and vanadium metal analyses, via inductively coupled plasma-atomic emission spectroscopy (ICP-AES) and sulfur by X-ray fluorescence spectroscopy (XFS). We also discussed the age of the crude oils, the origin of the materials, and the generation process in the presence of terpanes, hopanes, nickel, and vanadium.
Introduction Crude oils have their origin in the organic debris of plankton, algae, bacteria, and plants that inhabited the region in ancient times. Oil biomarkers originate from the microorganisms or the plants in the geological record1-3 that have carbon skeletons that can be related to a precursor molecule from a specific type of organism. The representative biomarkers are hopanes, norhopanes, oleananes, and steranes. The hopane series mainly originate from bacteria residues in carbonated or evaporated rocks and mud stone rocks. The hopanes are neither biodegraded nor denatured by the evaporation. Oleananes are one of the hopane series that originated from higher plants and are found significantly in southeast Asia crude oils. The steranes have a high contribution of organic matter from eukaryptic algaes and higher plants. In addition, the C27 hopanes, such as the trisnorneohopanes, originate from green algae or bacteria. *Author to whom correspondence should be addressed. Tel.: þ81-42-526-5634. Fax: þ81-42-526-5636. E-mail: masato-taki@ jcom.home.ne.jp. (1) Taguchi, K. Sekiyu no Seiin; Kyoritu Shuppan: Tokyo, 1998; p 27. (2) Peters, K. E.; Walters, C. C.; Moldowan, J. M. The Biomaker Guide; Cambridge University Press: New York, 2005; pp 3-616. (3) Waseda, A.; Nishita, H. Org. Geochem. 1998, 28, 27–41. (4) Douglas, G. S.; Owens, E. H.; Hardenstine, J.; Prince, R. C. Spill Sci. Technol. Bull. 2002, 7, 135–148. (5) Barakat, A. O.; Mostafa, A. R.; Qian, Y.; Kennicutt, M. C., II. Spill Sci. Technol. Bull. 2002, 7, 229–239. (6) Maki, H.; Sasaki, T. Mizukankyo Gakkai Shi 1997, 20, 9–13. (7) Zakaria, M. P.; Horinouchi, A.; Tsutsumi, S.; Takada, H.; Tanabe, S.; Ismail, A. Environ. Sci. Technol. 2000, 34, 1189–1196. (8) Kayukova, G. P.; Gordadze, G. N.; Nigmedzyanova, L. Z.; Kiyamova, A. M.; Romanov, A. G.; Zaripova, S. K.; Naumova, R. P. Petrol. Chem. 2006, 46, 1–8. r 2009 American Chemical Society
(9) Hardaway, C.; Sneddon, J.; Beck, J. N. Anal. Lett. 2004, 37, 2881– 2899. (10) Merryfield, R. N.; Loyd, R. C. Anal. Chem. 1979, 51, 1965–1968. (11) Nakayama, K.; Okada, S.; Tanaka, S. Bunseki Kagaku 1997, 46, 599–604.
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Experimental Section
Table 1. Classification of the Crude Oils
Crude Oil Samples and Reagents. Forty-one crude oils imported into Japan were obtained from five oil refinery companies in Japan (Cosmo Oil Co., Idemitsu Kosan Co., Kigunasu Sekiyu K.K., Nippon Oil Corp., and Showa Shell Sekiyu K.K.); they are described in Table 1. These crude oils were imported into Japan and represent more than 80% of all crude oils received in October 2007. The authentic standards of 18R22,29,30-trisnorneohopane (1), 17R-22,29,30-trisnorhopane (2), 17R-21β (H)-norhopane (3), oleananes (18R- and 18βoleanane) (4), and 17R-21β(H)-hopane (5) were purchased as a Hopane Kit from Chiron, Norway. The solvents, such as xylene and hexane, were purchased from Wako Pure Chemical, Ltd. (Tokyo, Japan). The standard materials for nickel and vanadium (22 ppm Ni and 52 ppm V (Lot No. 06MH005)) were purchased from Tokyo Chemical, Ltd. (Tokyo, Japan) and officially recognized by the Japan Petroleum Institute. Preparation and Analysis of Hopanes in Crude Oils by GC-MS. Each crude oil sample (0.200 g) was dissolved in 2 mL of hexane and then separated at 7000 rpm for 10 min, using a centrifugal separator using the same separation procedure for hexane-soluble material and insoluble residue in heavy oils, instead of the method of extraction and fractionation. The soluble material in the 200-μL hexane solution was transferred onto the top of the solid-phase extraction cartridge filled with 0.69 g of silica gel (Waters Corp.), which had been previously washed with 5 mL of hexane. The solution was eluted with 5 mL of hexane to isolate the saturated hydrocarbons, and the solvent was then evaporated using the centrifugal evaporator. The residue was also dissolved in hexane and added to the hexane fraction for a subsequent instrumental analysis. The hexane fractions containing the hopane homologous series were analyzed using the Yokogawa Analytical Systems eqiupment (Models HP5972 and HP5890), equipped with a J&W Scientific Durabond fused-silica capillary DB-1 column with an inner diameter (id) of 0.25 mm, a film thickness of 0.25 μm, and a length of 60 m, using a helium carrier gas (1.1 mL/min). The GC-MS operating conditions in the electron impact (EI) mode were an ionization potential of 70 eV with the ion source at 180 °C and the electron multiplier voltage at ∼2 keV. The injection port was maintained at 300 °C, and the sample (1 μL of a 5% (w/v) solution) was injected in the splitless mode, followed by a purge for 1 min after the injection. The column temperature was increased from 80 °C to 200 °C at a rate of 8 °C/min and then programmed to 300 °C at a rate of 4 °C/min. A selected-ion monitoring method was applied after a delay of 7 min, and the hopanes (including triterpanes) were quantified at m/z = 191. The peaks were identified by comparison of their retention times to those for the standards and their mass spectra, which were obtained from a different GC-MS run in the scan mode with the retention times reported in the literature.2,12-14 The five hopanes (1-5) previously mentioned and other compounds numbered at m/z 191, such as the C23 tricyclic terpane, C24 tricyclic terpane, C25 tricyclic terpane, C24 tetracyclic terpane, (22S)-17R-21β(H)-29-homohopane, (22R)-17R-21β(H)29-homohopane, (22S)-17R-21β(H)-29-bishomohopane, (22R)17R-21β(H)-29-bishomohopane, (22S)-17R-21β(H)-29-trshomohopane, (22R)-17R-21β(H)-29-trishomohopane, (22S)-17R21β(H)-29-tetrakishomohopane, (22R)-17R-21β(H)-29-tetrakishomohopane, (22S)-17R-21β(H)-29-pentakishomohopane, and (22R)-17R-21β(H)-29-pentakishomohopane were observed in Figure 1A. These 14 compounds were not considered in detail in this study, because they were present in very small amounts
abbreviation
classification
country
crude oil
Middle East Region northern Middle East IR-FB K-KU N-HU N-KF N-RA S-AH S-AM eastern Middle East IR-IH IR-IL IR-SI U-DB O-OM southern Middle East Q-QL Q-QM S-AL S-AX U-MB
a a a a a a a
Iran Kuwait Neutral Zone Neutral Zone Neutral Zone Saudi Arabia Saudi Arabia
Forozan-blend Kuwait Hout Khafji Wafra Arabian-heavy Arabian-medium
b b b b
Iran Iran Iran United Arab Emirates Oman
Iranian-heavy Iranian-light Sirri Dubai
b c c c c c
U-MU
c
U-UM
c
U-UZ
c
U-ZA
c
Qatar Qatar Saudi Arabia Saudi Arabia United Arab Emirates United Arab Emirates United Arab Emirates United Arab Emirates United Arab Emirates
Oman Qatar Qatar-marine Arabian-light Arabian-extra-light Murban Mubarras Umm-shaif Upper-zakum Zakum
Southeast Asia Region Borneo B-SE IN-AT IN-BU IN-HD MA-ML MA-RV MA-TP V-BA Sumatra IN-DU IN-SL IN-ST IN-WD
d d d d d d d d
Brunei Indonesia Indonesia Indonesia Malaysia Malaysia Malaysia Vietnam
Seria-light Attaka Bunju Handil Miri-light Labuan-light Tapis-blend Bach-ho
e e e e
Indonesia Indonesia Indonesia Indonesia
Duri Sumatra-light Cinta Widuri
China China China China
C-BL C-SR C-TC
e e e
G-RB
e
R-EB R-RO
e e
Russia Russia Russia
Ekhabinskaya Russian
ME-IS ME-MY
f f
Mexico Mexico Mexico
Isthmus Maya
Gabon/Africa Gabon
Bohai-light Shengli Taching Rabi-export blend
and produced little understanding about the discrimination of crude oils. Preparation and Analysis of Nickel and Vanadium by ICPAES and Sulfur by XFS. The metals in the crude oils are measured using a spectrophotometer and an atomic absorption spectrophotometer. These analyses are performed by the ashing
(12) Moldowan, J. M.; Dahl, J.; Huizinga, B. J.; Fago, F. J.; Hickey, L. J.; Peakman, T. M.; Taylor, D. W. Science 1994, 265, 768–771. (13) Subroto, E. A.; Alexander, R.; Kagi, R. I. Chem. Geol. 1991, 93, 179–192. (14) Chakhmakhchev, A.; Suzuki, M.; Waseda, A.; Takayama, K. Org. Geochem. 1997, 27, 523–536.
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Jurassic period of the Mesozoic era. The northern Middle East, such as Kuwait, the Neutral Zone, and Iran, contained crude oils that were mainly generated in the Cretaceous period of the Mesozoic era.15 These strata would discriminate the hopane distribution of crude oils in the northern Middle East (classification a) and the southern Middle East (classification c), although there was little or no relationship for the 3/5 and 4/5 ratios . The relationship between the 3/5 and 4/5 ratios is shown in Figure 2. The low 4/5 ratio was significant in the Middle East crude oils (classifications a-c), the Mexico crude oil (classification f), and the Sumatra Island, China, and Russia crude oils (classification e). All the crude oils are classified into three groups; (a-c, f), (d), and (e). Figure 3 shows the relationship between the 1/2 and 3/5 ratios in (a-c, f) of the 41 crude oils, to classify the Middle East crude oils more clearly into three groups than the classification of the 3/5 and 4/5 ratios. Compounds 1 and 2 were contained in a relatively small amount in all the crude oils. However, the 1/2 ratio was divided into the northern Middle East crude oils (classification a) and Mexico crude oils (classification f), eastern (Zagros suture zone and Oman) (classification b), and the southern part (classification c) among the Middle East crude oils. Compounds 1 and 2 are not affected by the biodegradation, but 1 showed a maturity of a greater thermal stability than 2.2,16 Compound 1 originated from green algae or bacteria2,17 and was extensively contained in the northern Middle East crude oils (classification a; see Figure 3), which resulted from green algae or bacteria undergoing maturity with more thermal stability. Simoneit et al.17 reported that the presence of tricyclic terpane hydrocarbons in Tasmanite algae provides an explanation of the oil origin in the Permian age. The southern crude oils originated from bacteria residues in the anoxic carbonate or marl source rock. The 1/2 ratio is controlled, to some degree, by the environment during deposition. Distribution and Composition of Nickel and Vanadium in Crude Oil. Porphyrins, which are tetrapyrrolic compounds, occur as free-base species,2 or naturally as metal complexes (e.g., nickel and vanadium), which were reported to be produced by the thermal decomposition of chlorophyll with cyanobacteria as plant-plankton in the Cretaceous period of the Mesozoic era and subsequently changed.18 The concentrations and ratios of nickel and vanadium can be used to classify and correlate the crude oils.2 This analysis, which has used hopanes, was not able to differentiate the crude oils produced in the northern Middle East from that in Mexico, as other factors, such as nickel and vanadium metals and sulfur, are combined. The ICP-AES method using dilution with an organic solvent simply and rapidly determined the metals in the crude oils within a short time, which was adapted for this study. Nakayama et al.11 reported that the nickel/vanadium ratio using the ICP-AES method discriminated the Japanese domestic crude oils from the imported Saudi Arabia crude oils. The concentrations of nickel and vanadium in the Middle East and Mexico crude oils are
method after decomposition with acid. However, for the analytical method thast uses acid decomposition, a very long time is required for the treatments and contamination is caused by other elements. Therefore, we did not adopt these ashing and acid methods; instead, we used an organic solvent dilution/ ICP-AES method. In the preparation of the crude oil samples, particular attention should be given to the reduction of the viscosity effect. The samples were vigorously shaken for at least 3 min, directly transferred to a 50-mL test tube, and diluted by a factor of 10 times the original sample size with xylene. The samples were filtered to remove any insoluble residue from the xylene solution. The sample weight was determined after a general consideration of the nickel and vanadium concentrations and viscosity. The presence of Ni and V atoms was analyzed using a Shimadzu Model ICP-7500 device. The analytical conditions were as follows: wavelength, 221.647 nm for nickel, 292.403 nm for vanadium; rf power, 1.4 kW; coolant gas, 16.0 L/min; plasma gas, 1.40 L/min; carrier gas, 700 mL/min; purge gas mode; high torch-height mode. The calibration curves were done using the standard samples of nickel and vanadium, which were supplied from the Japan Petroleum Institute. The standard samples must be prepared just prior to the analysis. The reproducibility (coefficient of variation) was 3.7% for nickel and 2.4% for vanadium. The limits of the nickel and vanadium were 0.04 and 0.01 ppm, respectively, based on the background equivalent concentration. Sulfur was analyzed using a Horiba Model SLFA-1800 system. This is a simple measurement for the sulfur concentration in fuel oil and heavy oil. The analytical conditions were as follows: analysis time, 100 s; power, 8 kV and 300 μA; sample volume, 10 mL. The sulfur limit was 5 ppm.
Results and Discussion Distribution and Composition of Hopane Series in Crude Oil. Typical gas chromatograms of the hopane homologous series (m/z = 191) monitored by the mass selective detector are shown in Figure 1A for the Middle East crude oil (Kuwait, Kuwait (K-KU)) (spectrum a), the southeast Asia crude oil (Malaysia, Labuan-light (MA-RV)) (spectrum b), and (c) the Far East crude oil (Russia, Ekhabinskaya (REB)) (spectrum c). The structures of the hopane compounds (1-5) are shown in Figure 1B. Compounds 3 (17R-21β (H)norhopane, C29 hopane) and 5 (17R-21β(H)-hopane, C30 hopane) were predominant for K-KU, but 4 (oleananes) was hardly observed in spectrum a in Figure 1A. Compound 4 shows a regional character, and 2 was observed to a greater extent than 1 in K-KU. For MA-RV (spectrum b in Figure 1A), 4 and 5 were superior. For R-EB (spectrum c in Figure 1A), 5 was substantially present, but 3 and 4 had lower contents than those in K-KU and MA-RV, respectively. All the crude oils contained 3 and 5. Thus, the individual compound of the hopane series was characteristic of the oil stratum well of the crude oils. Compound 5 was selected as the standard material7,14 in this study for evaluation of the 3 and 4 distributions in the 41 crude oils. Compound 3 was contained in a large amount in the Middle East crude oils (see items labeled “a”-“c” in Figure 2). Compound 3 originated from the bacteria residues in the evaporate and carbonate source rocks before the Cretaceous age. The crude oils in classification d (Borneo Island) contained 4, which originated from the angiosperm (flower plants) before the Cretaceous period of the Mesozoic era. Compound 5 originated from bacteria residues in mud stone rock3 and was present in the crude oils. The southern Middle East crude oils, such as those from Saudi Arabia, Qatar, and UAE, mainly originated from bacteria generated in the
(15) Sekiyu Gakkai. Sekai no Dai-yuden; Gihoudo: Tokyo, 1984; pp 77-255. (16) Damste, J. S. S.; Kuypers, M. M. M.; Pancost, R. D.; Schouten, S. Org. Geochem. 2008, 39, 1703–1718. (17) Simoneit, B. R. T.; Leif, R. N.; Neto, F. R. A.; Azevedo, D. A.; Pinto, A. C.; Albrecht, P. Naturwissenschaften 1990, 77, 380–383. (18) Ohkochi, N.; Kashiyama, Y.; Kuroda, J.; Ogawa, N.; Kitazato, H. Biogeosciences 2006, 3, 467–478.
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Figure 1. (A) m/z191 mass chromatograms of (a) Middle East crude oil (Kuwait, (K-KU)), (b) southeast Asia crude oil (Malaysia, Labuan-light (MA-RV)), and (c) Far East crude oil (Russia, Ekhabinskaya (R-EB)). (B) Structures of hopane compounds. (Legend for both panels: 1, 18R22,29,30-trisnorneohopane (Ts); 2, 17R-22,29,30-trisnorhopane (Tm); 3, 17R-21β(H)-norhopane (C29 hopane); 4, oleanane (18R-oleanane, 18β-oleanane); and 5, 17R-21β(H)-hopane (C30 hopane)).
shown in Figures 4 and 5. In Figure 4, the nickel concentration in the Middle East crude oils varied from almost zero
(
