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Chemical Composition of Athabasca Bitumen: The Distillable Aromatic Fraction Otto P. Strausz,*,† Elizabeth M. Lown,† Angelina Morales-Izquierdo,† Najam Kazmi,† Douglas S. Montgomery,† John D. Payzant,† and Juan Murgich‡ † ‡
Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2, Canada Centro de Química, Instituto Venezolano de Investigaciones Científicas (IVIC), Apartado 21827, Caracas 1020A, Venezuela ABSTRACT: The volatile aromatic fraction (240 °C and 103 Torr pressure) of Athabasca bitumen was separated via thinlayer chromatography (TLC) (Ag+/SiO2), followed by alumina column chromatography, into 13 mono-, di-, and triaromatic subfractions, each of which was subjected to field ionization mass spectrometry (FIMS) analyses. Altogether, close to 6000 constituent molecules, ranging in molecular weight from 200 to ∼800 Da, have been observed, including the partially and fully aromatized, ring-opened, and truncated derivatives of essentially all of the saturated biomarkers detected here or earlier in the saturated fraction of this bitumen. All molecules detected were of aromatic character, with the exception of a complex suite of cyclic terpenoid (and steroid) sulfides, having adsorptive properties similar to those of the triaromatic hydrocarbons. In several cases, the FIMS analyses were supplemented by conventional biomarker analyses and a novel biomarker analysis, employing basic aqueous extraction of the whole oil sands. The high-molecular-weight portion (MW > 482 Da) of each subfraction isolated (which usually does not show up in conventional biomarker analyses) varies in concentration from a few to about 10 wt %. This fraction may arise from processes analogous to the combination reactions occurring in the addition of biomarker molecules to asphaltene by CC, CSC, and COC covalent bond formation. In the present system (with the exception of the cyclic sulfides), only CC bond additions can be operative.
’ INTRODUCTION The present paper is a continuation of a series of papers on the chemical composition of Athabasca bitumen present in the gigantic oil sand accumulations in northnortheastern Alberta, Canada. Part 1 of this series (10.1021/ef100702j)1 reported the experimental methods employed in these studies along with a detailed description of the chemical composition of the saturate fraction of the bitumen. In the present paper, we report the chemical composition of the distillable portion of the aromatic fraction of the same bitumen from Athabasca. Crude oils are far too complex mixtures for any single-step approach in their chemical compositional studies. This complexity requires some preliminary partitioning of the constituent molecules into narrow fractions. Consequently, in our investigation of the chemical composition of Athabasca bitumen, as reported in part 1 of this series of papers (10.1021/ef100702j),1 we carried out extensive fractionation of the bitumen involving solvent precipitation/extraction, adsorption, complexation, and adduction chromatography, along with molecular distillation, following separation of the asphaltene from the maltene.1 Altogether, 15 silica gel column chromatographed fractions were collected, as described in part 1 (10.1021/ef100702j), each of which was subjected to molecular distillation (240 °C and 103 Torr), yielding 15 distillable and 15 non-distillable fractions [Figure 1 and Table 1 in part 1 (10.1021/ef100702j)]. The nonpolar fractions elutable with n-pentane (n-C5) and mixtures of n-pentane and benzene (Bz), Table 1, were further fractionated into varying numbers of subfractions. Thus, fraction 1 was r 2011 American Chemical Society
Table 1. Silica Gel Chromatographic Separation of the Aromatic Fraction of Athabasca Bitumena volume distillate as a percentage fraction
a
solvent
color of
(mL)
of bitumen (%)
distillate clear pale yellow
1
n-C5
750
26.7
2
10% Bz/n-C5
750
14.5
clear yellow
3
15% Bz/n-C5
750
2.1
clear orange
n-C5 = n-pentane.
Table 2. Refractionation of the Saturate Fraction 1 Using Ag+/TLC percentage of
percentage of
subfraction Rf range fraction 1 maltene (%)
bitumen (%)
la
56.4
18.2
15.1
colorless
1b
0.60.85
1.6
0.5
0.4
colorless
1c
0.30.6
25.0
8.1
6.7
colorless
1d
0.00.3
17.0
5.5
4.5
pale yellow
100.0
32.3
26.7
total
0.851.0
color
separated into four subfractions, Table 2, using Ag+/thin-layer chromatography (TLC). Received: June 6, 2011 Revised: August 25, 2011 Published: August 25, 2011 4552
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Table 3. Elemental Composition of Aromatic Subfractionsa,2 fraction
sample
monoaromatic diaromatic polyaromatic a
C (wt %)
H (wt %)
N (wt %)
O (wt %)
S (wt %)
H/C atomic ratio
MW (g mol1) 340
Athabasca
87.7
11.7
0.6
0.26
1.60
Cold Lake
87.8
11.8
0.65
0.74
1.60
Athabasca
87.6
10.6
0.6
2.4
1.46
Cold Lake
87.6
10.7
0.8
2.2
1.46
Athabasca
81.3
9.8
0.13
2.0
7.1
1.44
Cold Lake
81.6
9.6
0.16
2.5
6.7
1.41
380 490
USBM API-60 separation.2b
Table 4. Some Comparative Data on the Saturated and Aromatic Fractions3 C (wt %)
H (wt %)
N (wt %)
O (wt %)
S (wt %)
MW (g mol1)
(H/C)at
saturated
85
12.9
0.0
0.0
0.15
385
1.82
aromatics
8188
9.611.7
00.16
0.62.5
0.266.7
>365
1.411.6
pour point (°C)
viscosity SUS at 38 and 99 °C
API gravity (deg)
saturated
55
tri- > mono- > tetra- > penta- > hexa- > heptacyclics, which is similar to that found for the saturates: bi- > tri- > tetra- > penta- > mono- > hexa- > heptacyclics or acyclics. The concentration distributions as a function of the carbon number are again quite similar to what we have encountered in the saturates; that is, the maxima occurred at the carbon numbers, as listed in Table 13. The close analogy between the concentration distributions (by both ring number and carbon number) in the monoaromatics and the saturates again points to a genetic relationship between the two fractions, suggesting that the aromatic fraction was formed mainly by aromatization of the saturates. Fraction 2 is another major aromatic fraction of the bitumen, comprising 19.2% or, after molecular distillation, 14.5% of the bitumen. It consists mainly of diaromatic hydrocarbons, lesser amounts of monoaromatic hydrocarbons and even lesser amounts of triaromatic hydrocarbons, along with copious quantities of sulfur compounds, including alkylbenzothiophenes, dibenzothiophenes, and their naphtheno and higher benzo derivatives (Table 14). The concentration distribution with respect to ring number follows the order tri- > bi- > mono- > tetracyclics. This pattern of distribution is different from that of the monoaromatics; nonetheless, the fraction on the whole also exhibits a definite correlation with the saturates within the 4575
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in this series, which deals with the chemical composition of the polar (resin) fraction. The rest of this subfraction appears to be composed of a large number of alkyl-substituted tri- and tetra-aromatic compounds involving triaromatic steroid and tetra-aromatic hopanoid hydrocarbons, some novel condensed thiophenes with structures related to hopanes, aromatized hexacyclic sulfides and possibly disulfides with structures related to the hexacyclic sulfides found in subfraction 3b, and some carbazoles and carbazoles with a condensed naphthenic ring, corresponding to the series formula CnH2n17N. The bulk of the carbazoles is concentrated in the more polar fractions, as will be seen in part 3. One series of diaromatic hydrocarbons, the alkylated fluorenes, on account of their rare occurrence in nature and relatively high concentrations in Alberta bitumens, along with their alcoholic, ketonic, carboxylic, etc. derivatives, deserve special mentioning. The fluorene molecule, owing to the peculiarity of its electronic structure rendering the H(9) atoms somewhat acidic and their σ bonds somewhat weakened, exhibits an unusual reactivity.
The alkyl fluorenes elute from the alumina column with the diaromatic subfraction along with other Z = 16 compounds.
A few members of the Z = 16 family have been reported to be minor components of the aromatic hydrocarbons in crude oil26 and bitumen,27 but in general, fluorenes were considered to be only trace concentrations of petroleum until the discovery of relatively large concentrations of them28 and their derivatives29,30 in Athabasca bitumens. This was made possible by the acidity and consequent reactivity of fluorene and its exploitation for the isolation of these classes of molecules through a series of chemical transformations and GCSIR MS analyses. The high reactivity resides in the C9 position, and this position can be readily oxidized in a base-catalyzed reaction with molecular oxygen in the presence of a phase-transfer agent, such as 18-crown-6-ether.
Starting with a saturated cyclic biomarker, as the aromatization progresses, dealkylation and ring opening will take place as well and the maximum in the concentration versus the carbon number in the series plots will shift to smaller carbon numbers (Figures 28 and 29). Thus, in Figure 28, the maximum concentration in the saturated tetracyclic series occurs at C29, with a secondary maximum around C21, which is due to the partial loss of the isoprenoid side chain. As the aromatization progresses, the maximum shifts first from C29 to C21 and then to C19, owing to stepwise increasing dealkylation. Also, the pentacyclic series in the saturate fraction has its maximum at C30, which, similar to the tetracyclic series, shifts to C23 in the tetra-aromatic series, again because of the loss of the methyl groups and part of the alkyl side chain from the ring structure (Figure 29). The existence of these correlations lends strong support for the proposition that the bulk of the polycyclic aromatic hydrocarbons in subfractions 1c and d, subfraction 2, and as will be discussed below, subfraction 3 originated from the aromatization, ring cleavage, and dealkylation of saturated, mainly cyclic terpenoid, hydrocarbon-type biomarkers in the oil during thermal maturation. Subfraction 3 is a medium-size fraction in the bitumen, amounting to 5.8% of it. However, its volatility is low, with only 43% being distillable (corresponding to 2.1% of the bitumen). This subfraction (Table 15) contains several series of saturated cyclic sulfides ranging from two to six rings. They were first identified in Athabasca and other Alberta bitumens20 and oils and later shown to be ubiquitously present in all sulfurcontaining petroleum.2224 Their structure will be discussed in part 3
The oxidation of aromatics yielded a mixture of methylated fluorenones, 9-n-alkylfluorene-9-ols, and nuclear methylated 9-n-alkyl-fluorene-9-ols. TLC and cross-scan MS chromatograms for the isolated fluorenone fraction are shown in Figures 30 and 31 for a bitumen sample taken from a depth of 35 m and in Figure 32 for the 9-n-alkylfluorenols. These molecules were originally present in the aromatic fraction of the bitumen as nuclear methylated fluorenes and 9-n-alkylfluorenes.
Series on oxidized fluorenes were also detected in significantly higher concentrations in the polar (resin) and thermal decomposition products of asphaltene. Evidently, the oxidation of fluorenes by molecular oxygen is a facile reaction occurring in the bitumen reservoir as well, and it can be used as an indicator of the oxidative history of reservoirs. The chemistry of fluorenes in the bitumen will be discussed more extensively in part 3 of this series of papers dealing with the polar (resin) fraction of the bitumen.
’ SUMMARY The Athabasca bitumen sample studied was found to contain 38.6% aromatics, which are defined in terms of a silica gel column and an Ag+ ion on silica gel thin-layer plate chromatographic separation scheme; 76.4% of this aromatic fraction is distillable at 240 °C and 103 Torr pressure. After further fractionation 4576
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Figure 30. GCMS cross-scan chromatograms of the molecular ions of fluorenones from the oxidation of the aromatic fraction of a fresh Athabasca sample.29
Figure 31. GCMS cross-scan chromatograms of the molecular ions of fluorenones from the oxidation of the aromatic fraction of an aged Athabasca sample.30
by alumina column chromatography, FIMS and high-resolution ElMS investigations of this distillable aromatic fraction revealed a complex mixture from mono- to tetra-aromatics, along with
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Figure 32. GCMS cross-scan chromatograms of the molecular ions of 9-nalkylfluoren-9-ols from the oxidation of the aromatic fraction of a fresh Athabasca sample.31
some penta-aromatic hydrocarbons and nitrogen and sulfur aromatics (carbazoles and thiophenes), with a total number of aromatic and naphthenic rings of up to six. In addition, novel series of naphthenic sulfides in the C12C35 range with two to six terpenoid rings featuring isoprenoid side chains were also found to be present. Structurally, these are saturated compounds and are unrelated to aromatics; however, their chromatographic properties make them elute with the diaromatics, and hence, they are mentioned here. The most abundant components of the aromatic fraction are the bi- and tricyclics and the bi- and triaromatics. Most of the hydrocarbons, the sulfides, and a portion of the sulfur aromatics are genetically related to the cyclic terpenoid hydrocarbons, which make up the bulk of the saturate fraction of the bitumen. They probably were formed by aromatization,31 isomerization, dealkylation, partial ring-opening, and sulfur incorporation reactions. Living organisms do not produce aromatic hydrocarbons in significant quantities; therefore, the abundance of aromatic components in the bitumen and petroleum, in general, is thought to be due to the thermocatalytic conversion of alkanes and naphthanes during the diagenetic and catagenetic processes. This genetic relationship with the saturates explains the close correlation that exists between the saturate and aromatic concentration distributions with respect to the carbon number in the molecule for the various ring number series and their trend with respect to the number of total rings (aromatic + naphthenic) in the molecule. In agreement with this conclusion, the NMR spectrum of the distillable aromatics shows that longchain n-alkyl moieties are not dominant structural elements and that the total alkyl content is low. The origin of the nitrogen heteroaromatics, the carbazoles, is less certain. A significant portion of the approximately 6000 component molecules observed have a MW well above those observed in conventional analyses, up to an average of 700 Da. The presence 4577
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Figure 33. GCFIMS scan of the C11, C14, C17, C20, C22, C26, and C32 tricyclic components of the thiourea adduct fraction.
of these high-MW components above ∼450 Da is attributed, in analogy with the presence of chemically bound biomarker molecules in asphaltene,16 to combination reactions between two (or more) of the lower MW constituent molecules, comprising the aromatized derivatives of most common saturated biomarkers as well as some new ones first discovered in Athabasca asphaltenes, along with compounds that were not observed in crude oils before. The yields of the presumed combination product is higher here than in the case of asphaltenes, which is in line with the expected thermocatalytic mechanism for their production, because contact with the dispersed or solid bedrock clay, carbonate, or heavy metal catalytic surfaces is more favorable in the bulk liquid phase than in the aggregate phase. Each of the 6000 parent ion peaks can be further resolved into a few to numerous peaks using the GCFIMS combination developed in Strausz’s laboratory3235 in the late 1970s and early 1980s. Additional resolution can be achieved with the aid of prior fractionation by adduction chromatography (molecular sieve, urea, thiourea, etc.). An example of the GCFIMS of the thiourea monoadducts for the tricyclic alkanes, CnH2n4, in the Cold Lake saturates was reproduced in ref 1 (only every third carbon species was shown). In this case, the single parent ion evident in each of the FIMS ion intensity peaks of the CnH2n4 tricyclane is split into twothree major and numerous minor peaks. The GCFIMS spectrum of the CnH2n4 tricyclane shown in Figure 33 indicates a very different composition. Despite its useful capabilities, there does not appear to be any extensive use of the GCFIMS method in petroleum science, and we are aware of only a few industrial-oriented applications of it.3638
’ EPILOGUE: POTENTIAL IMPLICATIONS The results reported in this paper have significant relevance to petroleum sciences and to all phases of the petroleum industry: exploration, recovery, upgrading, refining, and transportation. Petroleum sciences deal with all aspects of the formation and history of petroleum, from the deposition of biotic source materials to the status and condition of the oil-bearing reservoir rock. Bitumen, being a highly complex polydisperse megamixture of hydrocarbons and related substances, poses challenges to
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the chemist searching for a roadmap to some hidden rules, principles, or relationships in the intimidatingly chaotic scenery of composition. Also, engineers attempting to develop new, environmentally friendlier improved technologies for the production of higher quality, environmentally cleaner liquid fuels from bitumens require better knowledge and a deeper understanding of the chemical composition of bitumen and its manufactured products. With regard to bitumen in general, Athabasca bitumen is rich in aromatics, heteroatoms, NOS, and metals and low or devoid of alkanes that makes it an inferior crude oil. As for the theory of formation and history, the key is biomarker chemistry that searches for molecules that were synthesized by the living organisms, which provided the biotic source material for the oil. The bulk of the inventory of the biomarker molecules is made up of saturated hydrocarbons, which had retained some of the important structural characteristics of the original biomolecules during transformation of the original source molecule to a biomarker molecule preserved in the oil. The present day aggregate concentration of known biomarkers in crude oils or bitumens is quite low, probably not exceeding single-digit values. The question in the present instance is what about the rest of the 27.8% distillable aromatics. The answer, as we concluded from our correlation diagrams (Figures 1215, 28, and 29 and Figure 5 from ref 1), is that the bulk of distillable aromatics is made up from a series of partially or fully aromatized saturates and saturated biomarker molecules, a portion of which has not been previously identified in Athabasca bitumen or described in the literature, such as (1) mono-, di-, tri-, and tetra-aromatic hopanes,* (2) tetraaromatic hopane cyclic sulfides and disulfides,* (3) triaromatic hopane cyclic sulfides,* (4) 8,14-secohopane cyclic sulfides,* (5) tri- and tetra-aromatic 17,21-secophanes,* (6) monoaromatic hexacyclic polyprenoids,* (7) ring alkylated fluorenes and 9-alkyl fluorenes, (8) although not aromatic, the di-, tri-, tetra-, and hexacyclic terpenoid sulfides series, which report with Fraction 3, and (9) benzo- and dibenzothiophenes from various sources, with some of them being useful biomarkers, as will be shown in part 3 of this series (asterisks denote new biomarkers). The new biomarkers series found here are consistent with the biodegraded marine carbonate origin of the bitumen and will be useful to delineate additional details of its origin and history. Other compound class fractions, the polars (resins) and asphaltenes, are also rich sources of biomarkers, and an in depth discussion of the biomarker chemistry is planned after the publication of the chemistry of the polar and asphaltene installments. The cyclic sulfides described above represent a major portion of the easily removable sulfur in the bitumen. They, in general, can be removed by milder hydrodesulfurization than thiophenes. The composition of the aromatic fraction presented here should be useful in all kinetic model calculations for in situ combustion, steam-assisted gravity drainage (SAGD), thermal cracking, in situ cracking, hydrocracking, etc. operations. Lastly, a better knowledge of the molecular composition of the aromatic fraction will likely be useful in advancing the understanding of the highly complex solution physics of the bitumen, which affects every phase of the oil sand industry.
’ AUTHOR INFORMATION Corresponding Author
*E-mail:
[email protected]. 4578
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’ REFERENCES (1) Strausz, O. P.; Morales-Izquierdo, A.; Kazmi, N.; Montgomery, D. S.; Payzant, J. D.; Safarik, I.; Murgich, J. Energy Fuels 2010, 24, 5053–5072. (2) (a) Selucky, M. L.; Chu, Y.; Ruo, T. C.; Strausz, O. P. Fuel 1978, 57, 9–16. (b) Selucky, M. L.; Chu, Y.; Ruo, T. C.; Strausz, O. P. Fuel 1977, 56, 369–381. (3) Rubinstein, I.; Strausz, O. P. In Oil Sand and Oil Shale Chemistry; Strausz, O. P., Lown, E. M., Eds.; Verlag Chemie: Weinheim, Germany, 1977; pp 177189. (4) Bulmer, J. T.; Starr, J. Syncrude Analytical Methods; Syncrude Canada, Ltd.: Edmonton, Alberta, Canada, 1979. (5) Hoffmann, C. F.; Strausz, O. P. Am. Assoc. Pet. Geol. Bull. 1986, 70, 1113–1128. (6) Peters, K. E.; Moldowan, J. M. The Biomarker Guide; Prentice Hall: Englewood Cliffs, NJ, 1993. (7) Schaeffer, P.; Poinsot, J.; Hauke, V.; Adam, P.; Wehrung, P.; Trendel, J. M.; Albrecht, P.; Connan, J. Angw. Chem., Int. Ed. 1994, 33, 1166–1169. (8) Rullkotter, J.; Philp, P. Nature 1981, 292, 616–618. (9) Grice, K.; Schaeffer, Ph.; Schwark, L.; Maxwell, J. R. Org. Geochem. 1996, 25, 131–147. (10) Strausz, O. P.; Kazmi, N.; Morales-Izquierdo, A.; Lown, E. M. Combined Research Report to Alberta Oil Sand Technology Research Authority; Alberta Oil Sands Technology and Research Authority (AOSTRA): Edmonton, Alberta, Canada, July 1, 1994June 30, 1995; Agreement 1105. (11) Rubinstein, I.; Spyckerelle, C.; Strausz, O. P. Geochim. Cosmochim. Acta 1979, 41, 1–6. (12) Rubinstein, I.; Strausz, O. P. Geochim. Cosmochim. Acta 1979, 43, 1887–1893. (13) (a) Ekweozor, C. M.; Strausz, O. P. Advances in Organic Geochemistry; Bjoroy, M., et al., Eds.; Wiley-Heyden: Chichester, U.K., 1981; pp 746766. (b) Ekweozor, C. M.; Strausz, O. P. Tetrahedron Lett. 1982, 23, 2711–2714. (14) Samman, N.; Ignasiak, T.; Chen, C. J.; Strausz, O. P.; Montgomery, D. S. Science 1981, 213, 1381–1383. (15) Cyr, T. D. Alberta Oil Sands Technology and Research Authority (AOSTRA) Fellowship Report; University of Alberta: Edmonton, Alberta, Canada, June 1982. (16) Peng, P.; Morales-Izquierdo, A.; Hogg, A.; Strausz, O. P. Energy Fuels 1997, 11, 1171–1187. (17) Strausz, O. P.; Mojelsky, T. W.; Faraji, F.; Lown, E. M.; Peng, P. Energy Fuels 1999, 13, 207–227. (18) Peng, P.; Morales-Izquierdo, A.; Lown, E. M.; Strausz, O. P. Energy Fuels 1999, 13, 248–265. (19) Peng, P.; Fu, J.; Morales-Izquierdo, A.; Lown, E. M.; Strausz, O. P. Energy Fuels 1999, 13, 266–277. (20) Payzant, J. D.; Montgomery, D. S.; Strausz, O. P. Tetrahedron Lett. 1983, 24, 651–654. (21) Peng., P.; Morales-Izquierdo, A.; Fu, J.; Jiang, J.; Hogg, A.; Strausz, O. P. Org. Geochem. 1998, 28, 125–134. (22) Payzant, J. D.; Cyr, T. D.; Montgomery, D. S.; Strausz, O. P. Tetrahedron Lett. 1985, 20, 4175–4178. (23) Cyr, T. D.; Payzant, J. D.; Montgomery, D. S.; Strausz, O. P. Org. Geochem. 1986, 9, 357–369. (24) Payzant, J. D.; Cyr, T. D.; Montgomery, D. S.; Strausz, O. P. In Geochemical Markers; Yen, T. F., Moldowan, J. M., Eds.; Hardwood Academic Publishers: Chur, Switzerland, 1989; pp 133142. (25) Chaffee, A. L.; Hoover, D. S.; Johns, R. B.; Schweighardt, T. In Biological Markers in the Sedimentary Record; Johns, R. B., Ed.; Elsevier: Amsterdam, The Netherlands, 1986; p 335. (26) Hallett, D. J.; Onuska, F. I.; Comba, M. E. Mar. Environ. Res. 1983, 8, 73–85. (27) Poirier, M. A.; Bas, B. S. Fuel 1984, 63, 361–367. (28) Mojelsky, T. W.; Strausz, O. P. Org. Geochem. 1986, 9, 39–45. (29) Mojelsky, T. W.; Strausz, O. P. Org. Geochem. 1986, 9, 31–37.
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(30) Payzant, J. D.; Mojelsky, T. W.; Cyr, T. D.; Montgomery, D. S.; Strausz, O. P. Org. Geochem. 1985, 8, 177–180. (31) Peters, K. E.; Walters, C. L.; Moldowan, J. M. The Biomarker Guide; Cambridge University Press: New York, 2005; pp 89 and 90 and 2007; Vol. 2, p 580. (32) Hogg, A. M.; Payzant, J. D.; Rubinstein, I.; Strausz, O. P. Proceedings of the 27th Annual Conference on Mass Spectroscopy and Allied Fields; Seattle, WA, June 38, 1979. (33) Payzant, J. D.; Rubinstein, I.; Hogg, A. M.; Strausz, O. P. Chem. Geol. 1980, 29, 73–88. (34) Strausz, O. P.; Rubinstein, I.; Hogg, A. M.; Payzant, J. D. Proceedings of the American Nuclear Society Conference on Atomic and Nuclear Methods in Fossil Fuels Energy Research; Mayaguez, Puerto Rico, Dec 14, 1980. (35) Strausz, O. P.; Rubinstein, I.; Hogg, A. M.; Payzant, J. D. In Atomic and Nuclear Methods in Fossil Fuels Energy Research; Filly, R. H., Carpenter, B. S., Ragaini, R. C., Eds.; Plenum: New York, 1982; pp 409441. (36) Ha, H. Z.; Ring, Z.; Liu, S. Pet. Sci. Technol. 2008, 26, 7–28. (37) Barker, Y.; Ring, Z.; Iacchelli, A.; McLean, N.; Rahimi, P. M. Energy Fuels 2001, 15, 23–37. (38) Barker, Y.; Iachelli, A.; McLean, N.; Fairbridge, C. Energy Fuels 2001, 15, 996–1002.
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