Origin of unresolved complex mixtures (UCMs) in biodegraded oils: Insights from artificial biodegradation experiments

Fuel 231 (2018) 53–60

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Full Length Article

Origin of unresolved complex mixtures (UCMs) in biodegraded oils: Insights from artificial biodegradation experiments ⁎

Shou-zhi Hua, , Shui-fu Lia, Jiang-hai Wangb, Jian Caoc,

T

⁎

a

Key Laboratory of Tectonics and Petroleum Resources (China University of Geosciences, Wuhan), Ministry of Education, Wuhan 430074, China School of Marine Sciences, Sun Yat-Sen University, Guangzhou 510006, China c School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China b

A R T I C LE I N FO

A B S T R A C T

Keywords: Oil biodegradation UCM Artificial experiment GC × GC – TOFMS Saline lacustrine oil Jianghan Basin

The origin of unresolved complex mixtures (UCMs) in biodegraded crude oils is one of the most puzzling questions in petroleum geochemistry due to the difficulty in characterizing their compositions and formation routes but potentially possess abundant critical geochemical information. To improve the understanding of this issue, a normal crude oil from the Eocene of the Jianghan Basin (eastern China) and its sub-fractions were artificially biodegraded by the bacteria strain Pseudomonas sp., which was extracted from naturally biodegraded crude oils in the field. The biodegradation products were further analyzed using comprehensive two-dimensional gas chromatography linked with a time-of-flight mass spectrometric detector (GC × GC – TOFMS). Results show that the oil and its sub-fractions all experienced varying degrees of biodegradation. The saturated fraction underwent the most intense biodegradation, followed by the aromatic fraction, while the polar fraction was only slightly biodegraded. The composition of the biodegradation products from the saturated fraction was similar to that of the whole crude oil, while that from the aromatic fraction only showed similarities at the low-molecularweight range. Few hydrocarbons were identified in the biodegradation products of the polar fraction. This implies that UCMs in biodegraded oils are derived mainly from the biodegradation of the saturated fraction, whereas the aromatic fraction makes only a contribution to the low-molecular-weight components. Minor terpanes and phenanthrenes were produced through the biodegradation of the polar fraction, indicating their minimal contribution to UCMs. Thus, these compounds and their related parameters should be used with caution in biodegraded oil-oil and oil-source correlations.

1. Introduction

spectroscopy [17], and data processing methods [18]. The results show that UCMs are composed of a large number of hydrocarbons having the same or similar chemical properties, consisting mainly of branched and cyclic, aliphatic, and aromatic isomers. Saturates in UCMs consist mainly of resistant monoalkyl-substituted “T” branched alkanes, as well as monocyclic and bicyclic compounds [3,19,20]. Aromatics in UCMs are mainly alkyl-substituted mono-aromatic hydrocarbons [16,20–22]. Studies have shown that in UCMs these monomers often have a biogenetic significance and are sensitive to maturity and secondary alteration [16,19]. Therefore, their identification and the establishment of relevant geochemical parameters are important in understanding the origin of biodegraded oils when conventional geochemical parameters are inapplicable. In addition, some UCMs are toxic [21,23–25]. Therefore, understanding the origin of UCMs also has broad implications on pollution treatment for petroleum-related environmental issues. In summary, although UCMs could potentially yield enormous

Unresolved complex mixtures (UCMs), as proposed by Blumer et al. (1970), refer to the unidentified compound mixtures present in oils. They are frequently observed in gas chromatograms of biodegraded petroleum and hydrocarbon extracts of reservoir rock following the coelution of irresolvable compounds that form through biodegradation, producing the rising chromatographic baseline indicative of a UCM [1,2]. As UCMs are almost unidentifiable, the origin of UCMs is one of the toughest questions in petroleum geochemistry. However, this needs to be studied because it has been suggested that UCMs contain even up to 250,000 compounds [3], indicating that they potentially possess abundant critical geochemical information [4]. Since 1970, there have been many attempts to constrain the compositions and explore the applications of UCMs. A series of techniques have been employed in the study of UCMs, including liquid chemistry [5–8], chemical oxidation [7,9–11], chromatography [12–16],

⁎

Corresponding authors. E-mail addresses: [email protected] (S.-z. Hu), [email protected] (J. Cao).

https://doi.org/10.1016/j.fuel.2018.05.073 Received 8 April 2018; Received in revised form 11 May 2018; Accepted 14 May 2018 Available online 19 May 2018 0016-2361/ © 2018 Elsevier Ltd. All rights reserved.

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pollution [26–28]. Therefore, to improve the understanding of this critical issue, in this study, a crude oil and its sub-fractions are artificially biodegraded by the bacteria strain Pseudomonas sp., which was extracted from a naturally biodegraded crude oil in the field. We separated and analyzed the hydrocarbons in the biodegradation products to constrain the compositions and origin of UCMs.

normal crude oil

biodegradation

liquid column chromatography

liquid column chromatography saturates saturates & aromatics

aromatics

2. Samples and methods

NSOs

2.1. Samples

biodegradation, respectively

We collected a normal crude oil from the 3rd oil layer, member 4 of the Eocene Qianjiang Formation in Well G18X-1 (depth at 3332–3352 m), located in the Qianjiang Depression of the Jianghan Basin, China. This is a typical saline lacustrine petroleum system in China [29]. The oil has a density of 0.85 g/cm3, viscosity of 12.1 mPa·s, freezing point of 30 °C, and sulfur content of 0.25%. After asphaltene precipitation from the oil by dissolving the oil in nhexane, the resulting bitumen was separated into the saturated, aromatic, and polar fractions by column chromatography on a 200 mesh silica gel using n-hexane, n-hexane and dichloromethane (nhexane:DCM, 2:1 v/v), and absolute ethanol and chloroform (ethanol: chloroform, 1:1 v/v) as eluents, respectively. After multiple separations, the collected masses of the saturated, aromatic, and polar fractions were all > 5 g. As the bacteria strain employed cannot degrade asphaltene [30], asphaltene was not prepared in this study (Fig. 1).

hydrocarbons extracted by chloroform

general characteristics by GC

individual compounds characterized by GC GC-TOFMS

Fig. 1. Generalized scheme for sample preparation and analysis used in this study.

amounts of geochemical information, their constituents and origins remain enigmatic, concealed by their complex compositions. The fact that a large amount of inaccessible geochemical information is unexploited has hindered the study of biodegraded oils and petroleum Res p o nse

G C Sat. HC o f O i l fr o m W el l G 18X- 1

Ph

800000

Res p o nse

A

750000

750000 700000

650000

650000

600000

nC17

550000

600000

nC22

500000

550000 500000

Pr

450000

450000

400000

400000

nC28

350000

350000 300000

300000

250000

250000

-Carotane

200000

Time (min)

5.00

Abundance 7000

10.00

15.00

20.00

25.00

30.00

35.00

40.00

45.00

50.00

55.00

6000

65.00

100000 Time (min)

25000

C23 TT

5500 5000 4000

C24 TeT

C22 TT

C25 TT

1000

Tm C26 TT C28 TT

500

Abundance

C

30.00

35.00

40.00

45.00

C33 H C34 H C35 H

45.00

50.00

50.00

55.00

60.00

m/z = 128, 142, 156, 170, 184

E

TMN

MN Naphthalene 0 Time (min) 11.00 12.00 13.00 14.00 15.00 16.00 17.00 18.00 19.00 20.00 21.00

60.00

C29 Ster C27 Ster

Abundance Phenanthrene

26000 22000

C28 Ster

3500

m/z = 178, 192, 206, 220

MP

F

18000

3000 2500

DMP

14000

C22 Ster

10000

1500 1000

6000

TMP

500 0 Time (min) 36.00

55.00

5000

Ts

C21 Ster

2000

40.00

10000

C32 H

m/z 217 Sat. HC of Oil from Well G18X-1

4500

25.00

TeMN C31 H

2500

35.00

20.00

15000

C29 H

C24 TT

3000

0 Time (min)

15.00

DMN

3500

C19 TT

10.00

20000

C20 TT C21 TT

4500

5.00

Abundance

C30 Gam

B

6500

60.00

C30 H

m/z 191 Sat. HC of Oil from Well G18X-1

7500

4000

200000 150000

150000

1500

Phenanthrene

D

800000

700000

2000

G C: Ar o . HC o f O i l fo r m W el l. G 18X- 1

850000

38.00

40.00

42.00

44.00

46.00

48.00

50.00

52.00

54.00

2000 Time (min) 22.00

23.00

24.00

25.00

26.00

27.00

28.00

29.00

30.00

31.00

32.00

Fig. 2. Gas chromatogram (A) and m/z 191 mass chromatogram (B) of saturates showing the distribution of tricyclic terpanes and pentacyclic terpanes; m/z 217 mass chromatogram (C) showing the characteristics of steranes; gas chromatogram (D), mass chromatograms of naphthalene and alkyl-naphthalenes (E) and phenanthrene and alkyl-phenanthrenes (F) of aromatics. Oil from Well G18X-1. 54

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Fig. 3. GC × GC–TOFMS TICs showing the hydrocarbon compounds from biodegraded whole oil (A), biodegraded saturates (B), biodegraded aromatics (C), and biodegraded polar fraction (D) from Well G18X-1.

programmed to increase from 60 °C (held for 2 min) to 150 °C at 8 °C/ min and then heated further to 320 °C (held for 10 min) at 3 °C/min.

2.2. Methods 2.2.1. Oil biodegradation and separation of biodegradation products We have isolated bacteria from the wellhead soil of a production well in the study area and obtained three types of bacteria, of which Pseudomonas sp. has the highest capability of hydrocarbon degradation [30,31]. Thus, we chose the bacteria with the highest biodegradation rate of oil to conduct the artificial biodegradation experiments. The medium was sterilized and inoculated with Pseudomonas sp. One milliliter of the medium was added to 1 g of the crude oil, and the prepared saturated, aromatic, and polar fractions, in separate small beakers. We have carefully analyzed the products of biodegradation by GC day by day in the oil artificial biodegradation experiment. Results show that the distribution pattern and intensity of UCM have seldom changed since 25 days. As the focus of this study is UCM, we incubated the cultures at 28 °C for 4 weeks (> 25 days) in a shaking incubator (160 rpm). The medium contained 2.5 g/L KH2PO4, 0.2 g/L MgSO4, 3.0 g/L NH4NO3, 0.1 g/L FeSO4, 2.0 g/L K2HPO4, and 0.5 g/L peptone. The pH was 7.0. The biodegradation products of the oil and its sub-fractions were extracted using chloroform. We dried and re-dissolved the extracts in a minimal amount of a n-hexane:dichloromethane mixture (nhexane:DCM, 2:1 v/v). We passed the resulting solution through a precombusted silica-gel column using a mixture of n-hexane and dichloromethane as the eluent. The eluent was then collected and concentrated in gas chromatography vials.

2.2.3. Comprehensive two-dimensional gas chromatography–time-of-flight mass spectrometry (GC × GC–TOFMS) We analyzed the biodegraded products of the oil and its sub-fractions with GC × GC–TOFMS using a Leco Pegasus 4D system comprising an Agilent 7890 GC equipped with two chromatographic columns, a pulsed jet modulator, and a time-of-flight (TOF) mass spectrometer (MS). The first-dimensional separation was performed on a HP-5MS capillary column (60 m, 0.25 mm ID; 0.25 µm film thickness) and the temperature was programmed to increase from 80 °C (held for 2 min) to 300 °C (held for 25 min) at 2 °C/min. The second-dimension separation was performed on a DB-17ht capillary column (2 m, 0.1 mm ID; 0.1 µm film thickness) and the temperature was programmed to rise from 100 °C (held for 0.2 min) to 330 °C (held for 30 min) at 2 °C/min. Samples were injected in splitless mode at 310 °C and helium was used as the carrier gas in constant flow mode (1.5 ml/min). The temperature of the GC × GC modulator was kept 30 °C higher than that of the first column. The modulator period was 8.0 s, including 2.0 s of hot air blow. The temperature of the transfer line was set at 280 °C. The GC × GC was connected to a TOF mass spectrometer, which was operated in electron ionization mode at 70 eV, scanning a mass range of m/z 40–520 at a frequency of 100 Hz. The source temperature was set at 250 °C. A detector voltage of 1475 V was used with a solvent delay of 10 min. The data were collected and analyzed using Chroma TOF 4.51 software. Peak identification was carried out with reference to the embedded NIST05 library and published spectra in petroleum geology [32,33].

2.2.2. Gas chromatography–mass spectroscopy (GC–MS) The saturated and aromatic fractions were analyzed in full scan mode using an Agilent 6890 gas chromatograph (GC) coupled to an Agilent 5973N mass selective detector (MSD). The GC was fitted with a HP-5MS capillary column (30 m, 0.25 mm ID; 0.25 µm film thickness). The samples were injected in splitless mode and the injector was set at 310 °C. For the saturates component, the oven temperature was programmed to rise from 100 °C (held for 2 min) to 310 °C (held for 15 min) at 3 °C/min. For the aromatics, the oven temperature was

3. Results and discussion 3.1. Composition of the crude oil before biodegradation The crude oil shows a complete distribution of n-alkanes peaking at n-C21 (Fig. 2A). The alkanes after n-C20 show slight even–odd predominance with an odd-to-even predominance (OEP) value of 0.94. The 55

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A

B

F

Sat. HC

C

D

E

Crude oil

G

Aro. HC

Crude oil

Sat. HC

Aro. HC

H

Resin

Resin

Fig. 4. Chromatograms (TIC, m/z 93, and m/z 95) of biodegraded products for crude oil, saturates, aromatics and resins, respectively. A, B, C and D show the hydrocarbon characteristics of biodegraded oil, biodegraded saturates, biodegraded aromatics and biodegraded resins by TIC, respectively. E, F, G and H show the UCM characteristics of biodegraded oil, biodegraded saturates, biodegraded aromatics and biodegraded resins by m/z 93 and m/z 95, respectively.

and trimethyl-phenanthrene (Fig. 2F). The calculated MPI-1 value indicative of maturity is 0.45 and the corresponding Rc is 0.67% (MPI2 = 0.55, MPI-3 = 0.96), consistent with the maturity evaluated from the degree of sterane isomerization above.

sample is enriched in acyclic isoprenoids, as evidenced by distinct peaks of phytane, pristane, norpristane, isohexadecane, and farnesane. Phytane is dominant in the n-alkanes (Pr/Ph = 0.36). β-carotane is observed near n-C37 (Fig. 2A). These characteristics indicate that the collected crude oil is a normal oil formed in a strongly reducing environment with high salinity. Tricyclic terpanes show a comparable concentration to that of pentacyclic triterpanes. Gammacerane is evident, with the peak height close to C30 hopane (gammacerane index = 0.98). The homohopanes are evenly distributed (Fig. 2B), consistent with the interpretation of high salinity based on gas chromatograms above. The C24 tetracyclic terpane peak is obvious, indicative of some contribution from higher plants. Pregnane and homopregnane are abundant and their peak heights are close to those of regular steranes. The regular steranes with αααR configuration show a V-shaped pattern (C27 > C28 < C29). αααR-C27 is slightly more enriched than αααR-C29 (C27/C29 = 1.10; Fig. 2C). The degree of isomerization represented by the ratio of αααC29-S/(S + R) = 0.51 and C29-ββ/(αα + ββ) = 0.47 suggests that the oil is mature. In terms of aromatics, its component is dominated by naphthalene and phenanthrene homologues, peaking at phenanthrene (Fig. 2D). The naphthalene homologues are dominated by dimethyl-, trimethyl-, and tetramethyl-naphthalenes. Trimethyl-naphthalene is the most abundant and the proportions of naphthalene and methyl-naphthalene are very low (Fig. 2E). The phenanthrene homologues are dominated by phenanthrene, followed by methyl-phenanthrene, dimethyl-phenanthrene,

3.2. Total ion chromatograms of the biodegraded products Hydrocarbons in the biodegraded products of the oil and its subfractions (saturates, aromatics, and polar fractions) were extracted and analyzed using GC × GC–TOFMS. Results show that the hydrocarbons in the artificially biodegraded products of the oil (Fig. 3A) and its saturated fraction (Fig. 3B) have the most abundant identifiable compounds. They also show the similarity, especially in the middle area of the two-dimensional chromatograms. The biodegraded products of the aromatic fraction (Fig. 3C) also show similarity to the oil and saturated fractions for the low-molecular-weight compounds. However, fewer compounds were observed in the middle area. More aromatic compounds plot in the upper middle area. In contrast, the TIC of the polar fraction is quite different from that of the oil and saturated fractions (Fig. 3D). The one-dimensional chromatogram shows that the baseline of crude oil and its saturated fraction rises after 4000 s and UCM appears (Fig. 4A and B). The one-dimensional chromatogram of the aromatic fraction is similar to that of the whole oil to begin with (before 2000 s); however, the rise in baseline after 4000 s is not as significant as for the whole oil (Fig. 4C). The chromatographic baseline of the polar fraction 56

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A

B

E

Crude oil

F

Sat. HC

Crude oil

Sat. HC

C

Aro. HC

G

Aro. HC

D

Resin

H

Resin

Fig. 5. Chromatograms of m/z 191 and m/z 217 for biodegraded products for crude oil, saturates, aromatics and resins, respectively. A, B, C and D show the terpane characteristics of biodegraded oil, biodegraded saturates, biodegraded aromatics and biodegraded resins by m/z 191, respectively. E, F, G and H show the sterane characteristics of biodegraded oil, biodegraded saturates, biodegraded aromatics and biodegraded resins by m/z 217, respectively.

is almost flat (Fig. 4D). According to Ventural (2008), UCMs have different distribution patterns relating to the retention time of compounds comprising the UCMs, and three types of UCMs were proposed based on their different distribution patterns, which have diagnostic fragment ions [16]. The UCMs in this study belong to the Type I proposed by him, which have the diagnostic fragment ions of m/z 93 and m/z 95. Thus, we used m/z 93 and m/z 95 mass chromatograms to characterize the oil and bitumen fractions in this study. It is showed that oil and saturates have similarly amplified baselines (Fig. 4E and F). However, the UCM bump is barely observed in the mass chromatograms of m/z 93 and m/z 95 for the aromatic and polar fractions, especially the polar fraction (Fig. 4G and H). Thus, the UCMs observed in chromatograms of biodegraded oils are derived mainly from the degradation of the saturated fraction as well as a smaller contribution from the degradation of the aromatic fraction. In contrast, the contribution due to degradation of the polar fraction is very small, as the polar fraction normally contains many heteroatom compounds, making it resistant to biodegradation (Pseudomonas sp.) [34].

compounds for analysis. The mass chromatogram of m/z 191 for the crude oil (Fig. 5A) is the sum of the corresponding mass chromatograms of the saturated and aromatic fractions (Fig. 5B and C), and it has no relation with the degraded products of resin (Fig. 5D). In addition, the abundance of tricyclic terpanes relative to pentacyclic terpanes decreases along with the increase of biodegradation degree; this can also be observed for the series of methyl-phenanthrenes in aromatics (Figs. 2 and 5). These imply that the terpanes in the biodegraded crude oil are mainly a product of degradation of the saturated fraction, while degradation of the aromatic fraction provides the phenanthrene homologues (Fig. 5A–C). Similarly, the mass chromatogram of m/z 217 for the crude oil (Fig. 5E) is also the sum of the mass chromatograms of the saturated and aromatic fractions (Fig. 5F and G). The characteristics of terpanes and methyl-phenanthrenes discussed above can also be found, i.e., the abundance of low-molecular-weight steranes relative to the total steranes. This implies that the steranes in the biodegraded crude oil are mainly a result of degradation of the saturated fraction, while degradation of the aromatic fraction supplies aromatic steranes (Fig. 5E–G). These all suggest that the biodegradation of saturated fraction will supply the most UCMs found in the biodegraded oil. Moreover, the degradation of the polar fraction makes only a minor contribution to the UCM (Fig. 5H). Other mass chromatograms for different fragment ions further support these results, such as m/z 123 (Fig. 6A–D) and m/z 125 (Fig. 6E–H). They also indicate that the biodegradation of the saturated fraction of oil makes the most significant contribution to the UCMs

3.3. Mass chromatograms of fragment ions To further constrain the difference in the hydrocarbon compositions of artificial biodegradation products of crude oil and its sub-fractions, we extracted the mass chromatograms of different characteristic ion 57

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A

E

Crude oil

B

Crude oil

F Sat. HC

Sat. HC

C

G Aro. HC

Aro. HC

D

H Resin

Resin

Fig. 6. Chromatograms of m/z 123 and m/z 125 for biodegraded products for crude oil, saturates, aromatics and resins, respectively. A, B, C and D show the terpane characteristics of biodegraded oil, biodegraded saturates, biodegraded aromatics and biodegraded resins by m/z 123, respectively. E, F, G and H show the sterane characteristics of biodegraded oil, biodegraded saturates, biodegraded aromatics and biodegraded resins by m/z 125, respectively.

are easily detected in the biodegraded products of resins (Fig. 7D). This implies that the possibility of biodegradation process relative to remnants of oil is more likely on the terpanes detected in biodegraded products of resins in this study. In summary, we conclude that the hydrocarbons detected in the m/z 191 mass chromatograms for the biodegraded crude oil are contributed mainly by biodegradation of the saturated fraction, followed by a relatively smaller contribution from the aromatic fraction, which contributes primarily to the phenanthrene series compounds. The biodegradation of the polar fraction makes a small contribution to phenanthrene series compounds and to the terpanes detected in the biodegradation product of the crude oil.

present in the biodegraded oil. These results are even more obvious in the two-dimensional mass chromatograms. The mass chromatogram for the fragment ion m/z 191 of the biodegraded crude oil shows four clearly identifiable regions: the phenanthrene series, long-chain tricyclic terpanes, tetracyclic terpanes, and pentacyclic triterpanes (Fig. 7). The biodegradation product of the crude oil has compounds distributed in all four of these regions (Fig. 7A). However, no phenanthrene series compounds were observed in the m/z 191 mass chromatogram for the biodegraded saturated fraction. Conversely, tricyclic, tetracyclic, and pentacyclic terpanes were not detected in the biodegraded product of the aromatic fraction (Fig. 7B), while plentiful phenanthrene series compounds, including methyl-, dimethyl-, and trimethyl-phenanthrenes as well as long-chain alkyl-phenanthrenes such as C12-P, were identified (Fig. 7C). Only a small amount of phenanthrene series compounds and minor tricyclic terpanes were observed in the biodegraded products of the polar fraction for the mass chromatogram of m/z 191 (Fig. 7D). These compounds might be the remnants of original oils, given that the initial polar fraction used in this study is more than 1 g and thus some phenanthrene series compounds and terpanes were possibly commingled into the resin fractions. This possibility is seldom likely although cannot be fully precluded. First, there should be no terpanes in the polar fraction before artificial biodegradation, following elution of the crude oil using different solvents as eluents. Second, if the compounds in the biodegraded products of resins are remnants of the oils, the aromatics are most likely to have this characteristic, too. However, there are no clear signs of tricyclic terpanes in the high resolution chromatogram of the biodegraded products of aromatics (Fig. 7C). In contrast, terpanes

4. Conclusions We artificially biodegraded a normal crude oil and its sub-fractions and then used GC × GC–TOFMS to analyze the hydrocarbon compounds in the degradation products. We found that the UCMs in crude oil were derived primarily from the degradation products of the saturated hydrocarbon fraction combined with a lesser contribution from the aromatics at the low-molecular-weight range. The degradation product of the polar fractions only contributes a small amount of terpanes and phenanthrenes to the UCMs. These compounds and their related parameters should be used with caution in biodegraded oil-oil and oil-source correlations.

58

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A

Phenanthrene Series

C

Pentacyclic Triterpane

C1-P

C12-P

C3-P C4-P C -P C6-P 5

C8-P

C -P C9-P C10-P 11

Long Chain Tricyclic Terpanes

Long Chain Tricyclic Terpanes

Phenanthrene Series

C7-P

Tetracyclic Triterpane

Tetracyclic Triterpane

B

Pentacyclic Triterpane

Phenanthrene Series C2-P

D

Pentacyclic Triterpane

Tetracyclic Triterpane

Phenanthrene Series

Pentacyclic Triterpane

Tetracyclic Triterpane

Long Chain Tricyclic Terpanes

Long Chain Tricyclic Terpanes

Fig. 7. GC × GC–TOFMS contour chromatograms of m/z 191 for different biodegraded components of oil from Well G18X-1: biodegraded whole oil (A), biodegraded saturates (B), biodegraded aromatics (C), and biodegraded polar fraction (D).

Acknowledgements [12]

We thank associate principal editor Yasushi Sekine and two anonymous reviewers for their detailed and constructive comments that helped to improve the manuscript. We thank SINOPEC Jianghan oilfield company for providing the oil sample. This study was supported by the National Natural Science Foundation (Grant Nos. 41672136, 41572109 and 41472100).

[13]

[14]

References

[15]

[1] Gough MA, Rowland SJ. Characterization of unresolved complex mixtures of hydrocarbons in petroleum. Nature 1990;34:648–50. [2] Peters KE, Walters CC, Moldowan JM. Biomarkers and isotopes in petroleum exploration and earth history. Biomarker guide New York: Cambridge University Press; 2005. p. 475–1132. [3] Sutton PA, Lewis CA, Rowland SJ. Isolation of individual hydrocarbons from the unresolved complex hydrocarbon mixture of a biodegraded crude oil using preparative capillary gas chromatography. Org Geochem 2005;36:963–70. [4] Booth AM, Sutton PA, Lewis CA, Lewis AC, Scarlett A, Chau W, et al. Unresolved complex mixtures of aromatic hydrocarbons: thousands of overlooked persistent, bioaccumulative, and toxic contaminants in mussels. Environ Sci Technol 2007;41:457–64. [5] Ellis L, Alexander R, Kagi RI. Separation of petroleum hydrocarbons using dealuminated mordenite molecular sieve-II. Alkylnaphthalenes and alkylphenanthrenes. Org Geochem 1994;21:849–55. [6] Frysinger GS, Gaines RB, Xu L, Reddy CM. Resolving the unresolved complex mixture in petroleum-contaminated sediments. Environ Sci Technol 2003;37:1653–62. [7] Killops SD, Al-Juboori MAHA. Characterisation of the unresolved complex mixture (UCM) in the gas chromatograms of biodegraded petroleums. Org Geochem 1990;15:147–60. [8] Mao D, Van De Weghe H, Diels L, De Brucker N, Lookman R, Vanermen G. Highperformance liquid chromatography fractionation using a silver-modified column followed by two-dimensional comprehensive gas chromatography for detailed group-type characterization of oils and oil pollutions. J Chromatogr A 2008;1179:33–40. [9] Revill AT. Use of oxidative degradation followed by capillary gas chromatographymass spectrometry and multi-dimensional scaling analysis to fingerprint unresolved complex mixtures of hydrocarbons. J Chromatogr 1992;589:281–6. [10] Thomas KV, Donkin P, Rowland SJ. Toxicity enhancement of an aliphatic petrogenic unresolved complex mixture (UCM) by chemical oxidation. Water Resour 1995;29:379–82. [11] Warton B, Alexander R, Kagi RI. Characterisation of the ruthenium tetroxide

[16]

[17]

[18]

[19]

[20]

[21]

[22]

[23]

[24]

[25]

59

oxidation products from the aromatic unresolved complex mixture of a biodegraded crude oil. Org Geochem 1999;30:1255–72. Gough MA, Rhead MM, Rowland SJ. Biodegradation studies of unresolved complex mixtures of hydrocarbons model UCM hydrocarbons and the aliphatic UCM. Org Geochem 1992;18:17–22. Hu SZ, Li SF, Cao J, Zhang DM, Ma J, He S, et al. A comparison of normal and reversed phase columns in oil analysis by comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry. Pet Sci Technol 2014;32:565–74. Li S, Cao J, Hu S. Analyzing hydrocarbon fractions in crude oils by two-dimensional gas chromatography/time-of-flight mass spectrometry under reversed-phase column system. Fuel 2015;158:191–9. Tran TC, Logan GA, Grosjean E, Ryan D, Marriott PJ. Use of comprehensive twodimensional gas chromatography time-of-flight mass spectrometry for the characterization of biodegradation and unresolved complex mixtures in petroleum. Geochim Cosmochim Acta 2010;74:6468–84. Ventura GT, Kenig F, Reddy CM, Frysinger GS, Nelson RK, Mooy BV, et al. Analysis of unresolved complex mixtures of hydrocarbons extracted from Late Archean sediments by comprehensive two-dimensional gas chromatography (GC×GC). Org Geochem 2008;39:846–67. Mapolelo MM, Rodgers RP, Blakney GT, Yen AT, Asomaning S, Marshall AG. Characterization of naphthenic acids in crude oils and naphthenates by electrospray ionization FT-ICR mass spectrometry. Int J Mass Spectrom 2011;300:149–57. Demir C, Hindmarch P, Brereton RG. Deconvolution of a three-component coeluting peak cluster in gas chromatography-mass spectrometry. Analyst 2000;125:287–92. Li S, Cao J, Hu S, Luo G. Characterization of compounds in unresolved complex mixtures (UCM) of a Mesoproterzoic shale by using GC×GC-TOFMS. Mar Pet Geol 2015;66:791–800. Ventura GT, Simoneit BRT, Nelson RK, Reddy CM. The composition, origin and fate of complex mixtures in the maltene fractions of hydrothermal petroleum assessed by comprehensive two-dimensional gas chromatography. Org Geochem 2012;45:48–65. Melbye AG, Brakstad OG, Hokstad JN, Gregersen IK, Hansen BH, Booth AM, et al. Chemical and toxicological characterization of an unresolved complex mixture-rich biodegraded crude oil. Environ Toxicol Chem 2009;28:1815–24. Booth AM, Scarlett AG, Lewis CA, Belt ST, Rowland SJ. Unresolved complex mixtures (UCMs) of aromatic hydrocarbons branched alkyl indanes and branched alkyl tetralins are present in UCMs and accumulated by and toxic to, the mussel Mytilus edulis. Environ Sci Technol 2008;42:8122–6. Petersen K, Hultman MT, Rowland SJ, Tollefsen KE. Toxicity of organic compounds from unresolved complex mixtures (UCMs) to primary fish hepatocytes. Aquat Toxicol 2017;190:150–61. Reineke V, Rullkötter J, Smith EL, Rowland SJ. Toxicity and compositional analysis of aromatic hydrocarbon fractions of two pairs of undegraded and biodegraded crude oils from the Santa Maria (California) and Vienna basins. Org Geochem 2006;37:1885–99. Scarlett A, Galloway TS, Rowland SJ. Chronic toxicity of unresolved complex

Fuel 231 (2018) 53–60

S.-z. Hu et al.

[26]

[27] [28] [29]

[30] Wang ZY, Gu GZ, Su TT, Tang ZQ. Isolation of strain Pseudomonas sp. DY12 with degrading petroleum activity and studies on its degrading performance. Chem Bioeng 2009;26:67–9. [31] Deng MC, Li J, Liang FR, Yi M, Xu XM, Yuan JP, et al. Isolation and characterization of a novel hydrocarbon-degrading bacterium Achromobacter sp. HZ01 from the crude oil-contaminated seawater at the Daya Bay, southern China. Mar Pollut Bull 2014;83:79–86. [32] Philip RP. The spectrum and application of fossil fuel biomarkers (in Chinese). Beijing: Science Press; 1987. [33] Wang P. The mass spectrum criterion of petroleum biomarkers. Beijing: Petroleum Industry Press; 1993. [34] Xu F. Isolation and biodegradation characteristics and application of highly efficient petroleum degrading strains. Northwest A&F University; 2010.

mixtures (UCM) of hydrocarbons in marine sediments. J Soils Sediments 2007;7:200–6. Weng N, Wan S, Wang H, Zhang S, Zhu G, Liu J, et al. Insight into unresolved complex mixtures of aromatic hydrocarbons in heavy oil via two-dimensional gas chromatography coupled with time-of-flight mass spectrometry analysis. J Chromatogr A 2015;1398:94–107. López L, Lo Mónaco S, Volkman JK. Evidence for mixed and biodegraded crude oils in the Socororo field, Eastern Venezuela Basin. Org Geochem 2015;82:12–21. Reid AJ, Budge SM. Identification of unresolved complex mixtures (UCMs) of hydrocarbons in commercial fish oil supplements. J Sci Food Agric 2015;95:423–8. Li M, Chen Z, Cao T, Ma X, Liu X, Li Z, et al. Expelled oils and their impacts on RockEval data interpretation, Eocene Qianjiang Formation in Jianghan Basin, China. Int J Coal Geol 2018;191:37–48.

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