Chemical Composition of Athabasca Bitumen: The Saturate Fraction

Weslake , D. W. Private communication; University of Alberta, Edmonton, Alberta, Canada, 1978. There is no corresponding record for this reference. 28...
0 downloads 0 Views 3MB Size
Download PDF
Energy Fuels 2010, 24, 5053–5072 Published on Web 08/12/2010

: DOI:10.1021/ef100702j

Chemical Composition of Athabasca Bitumen: The Saturate Fraction Otto P. Strausz,*,† Angelina Morales-Izquierdo,† Najam Kazmi,† Douglas S. Montgomery,† John D. Payzant,† Imre Safarik,† and Juan Murgich‡ †

Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2, Canada, and ‡Centro de Quı´mica, Instituto Venezolano de Investigaciones Cientı´ficas (IVIC), Apartado 21827, Caracas 1020A, Venezuela Received June 7, 2010. Revised Manuscript Received July 26, 2010

Presented is an account of the bulk and molecular composition of the saturate fraction of Athabasca bitumen. It is shown that, for a clean isolation, it is necessary to subject the column-chromatographyseparated crude saturates to molecular distillation followed by a silver ion chromatography step. Upon field ionization mass spectrometry (FIMS) analysis, the molecular distribution of the purified saturates exhibits a pulsating character with near trace concentration at hexa- and heptacyclics and varying concentrations of mono- to pentacyclics, with bi-, tri-, and tetracyclic dominance. The overall distribution is bimodal and, in contrast to conventional gas chromatography (GC) or GC-mass spectrometry (MS) results, extends to m/z ∼750, having maxima at m/z ∼400 and 600, with a total concentration of 15.1% of the bitumen. A gamut of biomarker molecules has been identified, including drimanes, cheilanthanes, tetracyclic terpanes, 17,21- and 8,14-secophanes, steranes and diasteranes, hopanes, gammaceranes, hexahydrobenzohopanes, etc. GC-FIMS results indicate that over half a dozen isomers accompany nearly each of the identified biomarkers. Although biomarker chemistry lies outside the scope of the present paper (an item that will be dealt with in detail in a forthcoming paper), we briefly remark here that the overall distribution of the biomarkers detected is consistent with and thus lends support to the notion that Athabasca bitumen is the residue of the secondary microbiological degradation of mature/(early mature) marine carbonate oils formed in a strongly reducing depositional environment. Additionally, a useful novel method for the extraction of biomarkers from oil sands is reported.

hydrocarbons, and therefore, bitumens in general are devoid or strongly depleted of their paraffinic complement and belong to the naphthenic-aromatic class heavy crude oil family. They represent highly complex and variable mega-component mixtures of hydrocarbons and hydrocarbon-based molecules, with some organometallics in real solution as well as in the form of colloidal dispersions of aggregates.2,3 The present, first, and subsequent forthcoming papers deal with the composition and its underlying principles of Athabasca bitumen, a representative member of the high sulfur family of bitumens. Specifically, this paper reports on the composition of the saturate fraction of the same bitumen.

Introduction Alberta bitumen and heavy oil deposits represent one of the world’s largest known hydrocarbon accumulations, with about 1.7 trillion barrels of bitumen in sand rocks, the oil sands resources, and about 0.86 trillion barrels in carbonate rocks, the carbonate trend resources. Of the three major oil sand deposits of Alberta, the Peace River, Cold Lake, and Athabasca deposits, by far the largest one is the Athabasca deposit, with bitumen accumulation over half of the sum total.1 Bitumen is the heaviest form of petroleum, and similar to Alberta bitumen, all of the known massive bitumen accumulations in the world are the residues of the secondary microbiological degradation of conventional petroleums.2,3 They are dense, slightly viscoelastic, semi-solid hydrocarbons with a dark brown to black color, richly endowed with heteroatoms (N, O, and S), trace level metals, and organometallic compounds.3,4 Bitumens are defined as petroleums with viscosities >104 mP s and a density >1.000 g/cm-3, corresponding to American Petroleum Institute (API) gravity of less than 10. The microorganisms causing the secondary biodegradation of petroleum preferentially metabolize straight-chain paraffinic

Experimental Section The electron impact mass spectrometric determinations on saturates were performed on a KRATOS MS-50 instrument operating at a resolution of M/ΔM ≈ 10 000. The other instrument used was an MS-9 spectrometer modified for field ionization.4 This instrument was operated at a resolution of M/ΔM ≈ 1000. The emitters were of the activated tungsten wire type. During the experiment, the sample (typically 1.25 mg) was distilled from a direct insertion probe into the ion source. The probe temperature was raised at 2-6 C/min from ambient to 250 C. The ion source was maintained at a constant temperature of 240 C. During this time, 100-300 scans of the mass spectrum (m/z 28-750) were accumulated by a DS-555 data system. These were summed together to afford the averaged spectrum of the sample. The standard deviation of the peak intensities was estimated to be a few percentages of the base peak.

*To whom correspondence should be addressed. E-mail: opstrausz@ shaw.ca. (1) Meyer R. F. World heavy crude oil resources. Proceedings of the 15th World Petroleum Congress; Beijing, China, Oct 12-17, 1997. (2) Speight, J. G. The Chemistry and Technology of Petroleum, 4th ed.; CRC Press: New York, 2006. (3) Strausz, O. P.; Lown, E. M. The Chemistry of Alberta Oil Sands, Bitumens and Heavy Oils; Alberta Energy Research Institute: Calgary, Alberta, Canada, 2003. r 2010 American Chemical Society

(4) Payzant, J. D.; Hogg, A. M.; Montgomery, D. S.; Strausz, O. P. AOSTRA J. Res. 1984, 1, 175–182.

5053

pubs.acs.org/EF

Energy Fuels 2010, 24, 5053–5072

: DOI:10.1021/ef100702j

Strausz et al.

Table 1. Chromatography of the Maltene Fraction of Athabasca Bitumen on Silica Gel

fraction

solvent

1 2 3 4 5 6 7

n-C5 10% Bz/n-C5 15% Bz/n-C5 10% CH2Cl2/n-C5 25% CH2Cl2/n-C5 50% CH2Cl2/n-C5 50% CH2Cl2/n-C5

8 9

100% CH2Cl2 100% CH2Cl2

10 11 12 13 14 15 totals

10% ethyl acetate/CH2Cl2 10% ethyl acetate/CH2Cl2 1% i-propanol/CH2Cl2 2% CH3OH/CH2Cl2 2% CH3OH/CH2Cl2 15% CH3OH/CH2Cl2

volume (mL)

weight (g)

percentage of maltene (%)

percentage distilled (%)

distillate as a percentage of maltene (%)

750 750 750 1000 750 75 625

1.7885 1.1554 0.2909 0.0501 0.1573 0.1259 0.1987

35.8 23.1 5.8 1.0 3.1 2.5 4.0

≈90 76 43 54 55 15 37

32.2 17.5 2.5 0.5 1.7 0.38 1.5

pale yellow yellow orange orange

100 650

0.0734 0.1153

1.5 2.3

22 33

0.33 0.76

bright red dull red

75 675 600 1000 1000 650

0.3235 0.2089 0.0253 0.2145 0.1898 0.1451

6.5 4.2 0.5 4.3 3.8 2.9 101.2

25 31

1.63 1.3

54 57 33

2.3 2.2 0.96 65.76

Data processing is displayed as bar graphs. In these graphs, the mass spectrum (average of 100-300 scans) is displayed in the usual way. The measured relative abundance at each mass is plotted as a function of the mass number. All hydrocarbons may be represented by the generic formula CnH2nþZ, where n is the number of carbon atoms and Z reflects the hydrogen deficiency. In petroleum, the various classes of compounds present usually occur as a homologous series in n for each value of Z. It is convenient to display the variation of n for the various values of Z. This was performed by plotting the same data as for the previous display mode, but now every 14th point is joined by a straight line. This corresponds to increasing the value of n by 1 in the formula CnH2nþZ. The starting point was determined by the desired value of Z, which, for the saturated fraction, ranged from þ2 to -10, i.e., from zero to six rings. The gas chromatographic column used in the overall analysis was a 30 m  0.25 mm DB-1 bonded phase capillary column operated up to 290 C. The sample location was near Fort McMurray, Alberta, Canada, 18 m below the surface and was designated as Syncrude highgrade (SHG) oil sand containing 12% bitumen, which was removed from the oil sand by Soxhlet extraction with CH2Cl2. In the compound class study of the bitumen, the extract was diluted with an equal volume of CH2Cl2 and the asphaltene was precipitated with a 40-fold excess of n-pentane. The yield of the asphaltene was 17% of the bitumen. The resultant maltene was fractionated by elution chromatography on a silica gel (70-230 mesh, 2.5 cm  1 m) column, which was activated by heating for 24 h at 110 C. A 5 g sample of maltene was charged to the column (150 g of silica gel) in a solution of n-pentane and, subsequently, eluted with the series of solvents shown in Table 1. This solvent elution sequence removed essentially all of the material from the column. Each of the fractions 1-15, with the exception of fraction 12, was subjected to molecular distillation in a sublimation apparatus at 240 C at a pressure of 10-3 Torr to prepare the fractions for field ionization mass spectrometry (FIMS) analysis. The percentage of each fraction volatilized is shown graphically in Figure 1. In further refinement of the isolation of the saturate fraction, the crude saturate fraction, after molecular distillation, was rechromatographed on thin-layer plates to separate the aromatic, olefinic, and sulfur-containing compounds from the saturates. The plates used were 20  20 cm and were coated with a 1 mm layer of silica gel (Merck 60G catalog number 7731) impregnated with 10 wt % AgNO3. The plate was dried at 115 C for 1 h and then exhaustively eluted with ethyl acetate. The upper 1 cm of the plate was scraped off to remove impurities, and then the plate was activated by heating overnight at 115 C. Approximately 70 mg of

color of the distillate

comments

nitrogen compounds nitrogen compounds mixture of nitrogen compounds and fluorenones fluorenones mixture of fluorenones and fluorenols fluorenols complex mixture

carboxylic acids and sulfoxides

Figure 1. Graphical display of the distillation data from Table 1. Plot of the percentage of each fraction distilling up to a maximum pot temperature of 240 C and 10-3 Torr for fractions 1-15. Compounds heavier than C50 do not distill under this condition.

the crude saturate fraction was applied to the bottom of each plate, and the chromatogram was developed with distilled n-heptane. In this manner, the saturate fraction was divided into four broad subfractions, 1a-1d, as shown in Table 2. Experiments were also performed involving the whole oil sands. In these cases, the sands were extracted with dilute aqueous NaOH typically for 1 h at 80 C. The aqueous extracts were then separated from the sands and from the bitumen and then extracted with methylene chloride. Analyses of the organic contents were carried out after chromatographic fractionation using gas chromatography (GC) and GC-mass spectrometry (MS). Thiourea adduction (TUNA) was carried out as reported in ref 6b. (5) (a) Iha, K. N.; Montgomery, D. S.; Strausz, O. P. Prepr. Pap.— Am. Chem. Soc., Div. Fuel Chem. 1979, 24, 260–266. (b) Cheu, H. H.; Mojelsky, T. W.; Payzant, J. D.; Lown, E. M.; Henry, D.; Wallace, D.; Strausz, O. P. AOSTRA J. Res. 1991, 7, 17–35. (c) Choi, H. K. J.; McIntyre, D. D.; Montgomery, D. S.; Strausz, O. P. AOSTRA J. Res. 1987, 3, 125–130. (6) (a) Payzant, J. D.; Rubinstein, I.; Hogg, A. M.; Strausz, O. P. Chem. Geol. 1980, 29, 73–88. (b) Rubinstein, I.; Strausz, O. P. Geochim. Cosmochim. Acta 1979, 43, 1387–1392.

5054

Energy Fuels 2010, 24, 5053–5072

: DOI:10.1021/ef100702j

Strausz et al.

Figure 2. Capillary gas chromatograph of fraction 1a (Table 2). The peaks labeled B, T, and H are the bicyclic and tricyclic terpenoid hydrocarbons and the hopanes, respectively, and the subscript numbers indicate the number of carbon atoms per molecule. Table 2. Refractionation of the Saturate Fraction 1 Using Agþ Thin-Layer Chromatography (TLC) percentage percentage of maltene of bitumen subfraction Rf range fraction 1 (%) (%) la 1b 1c 1d

0.85-1.0 0.6-0.85 0.3-0.6 0.0-0.3

56.4 1.6 25.0 17.0 100.0

18.2 0.5 8.1 5.5 32.3

15.1 0.4 6.7 4.5 26.7

color colorless colorless colorless pale yellow

Results and Discussion Although the discussion will be confined to the saturated fraction 1a to show its relative importance in the maltene fraction, the percentages of all 15 fractions into which the maltene was fractionated by elution chromatography on silica gel are presented in Table 1 and Figure 1. Each of these fractions, numbered 1-15, was subjected to high vacuum distillation at 10-3 Torr up to a temperature of 240 C. Figure 1 illustrates the high degree of variability that exists in the proportion of each fraction that is capable of being distilled under these conditions. Approximately 90% of fraction 1 was distillable. The distillable part of fraction 1 was recognized as still containing small amounts of olefins as well as aromatic and sulfur-containing compounds;5 consequently, refractionation on a AgNO3 thin-layer plate was necessary to remove these materials to facilitate the interpretation of the mass spectral results. The resulting purified subfraction, fraction 1a, constitutes 18.2% of the maltene (Table 2) or 15.1% of the bitumen. Figure 2 shows the capillary flame ionization GC trace of fraction 1a, consisting a broad hump superimposed by numerous sharp peaks, some of which are assigned. The chromatogram indicates a complex mixture with a carbon number range of C10-C35. Details of the peak assignment will be discussed momentarily. The field ionization mass spectrum of fraction 1a is shown in Figure 3, and as may be seen from the valleys between successive peaks, certain Z members are preferred while others are missing or appear only at trace levels, resulting in a unique spectrum featuring periodic band progressions separated by deep valleys throughout the spectrum. If the distillation and

silver ion thin-layer chromatographic step in the purification of the crude saturates are omitted, then the spectrum takes on a more conventional appearance as seen in Figure 4. The major peaks in Figure 3 manifest the presence of a long series of one- to five-membered rings, with low levels of sixmembered rings and trace amounts of acyclic alkanes. As also evident from the spectrum, fragmentation, in contrast to the electron impact mass spectrum (EIMS), is minimal, which is one of the major advantages of the field ionization method. The other useful advantage is that the observed relative abundance of parent ions in a first approximation is independent of the molecular structure of the cycloalkanes. Thus, the concentration distribution of the mono- to hexacyclic alkanes according to carbon number can be readily derived from the FIMS spectrum along with the gravimetric composition and carbon number maxima.6a These quantities for Athabasca and Cold Lake saturates are presented in Figures 5 and 6 and Table 3. The comparative data in Table 3 show a higher yield of saturates (18.5 or 15.1%) and a skewed distribution favoring lower condensed molecules (with a Z number of þ2, 0, and -2; 57 versus 48%) and reflect the less severe biodegradative state (about 6 versus 8 on the Peter and Moldowan scale7) for the Cold Lake than the Athabasca bitumen. This conclusion is further supported by the appearance of acyclic isoprenoids,6 phytane (C20), and pristane (C19), along with a pattern of pairs of peaks at C24/C25, C29/C30, C34/C35, C39/ C40, and possibly C14/C15, resembling the distribution of C18C40 isoprenoid hydrocarbons found in conventional crude oils together with a higher concentration of n-alkanes (0.59 versus 0.04%), showing a smooth, unimodal distribution.8 Aside from microbial degradation states, the two saturate fractions bear a close resemblance. The maxima noted in Table 3 have relevance to their relation to the distribution of biomarkers in the saturate fraction, vi. In connection with Figure 3, it should be kept in mind that the mass peaks in the FIMS spectrum represent the sum of all isomeric molecules at any given molecular weight (MW) present in the sample material. Indeed, as the GC-FIMS results (7) Peters, K. E.; Moldowan, J. M. The Biomarker Guide; PrenticeHall: Englewood Cliffs, NJ, 1993. (8) (a) Selucky, M. L.; Chu, Y.; Ruo, T. C. S.; Strausz, O. P. Fuel 1978, 57, 9–16. (b) Selucky, M. L.; Chu, Y.; Ruo, T. C. S.; Strausz, O. P. Fuel 1977, 56, 369–381.

5055

Energy Fuels 2010, 24, 5053–5072

: DOI:10.1021/ef100702j

Strausz et al.

Figure 3. Field ionization mass spectrum of the subfraction 1a (Table 2). The peaks at m/z 208, 222, 236, etc. correspond to CnH2n-2 (bicyclic) compounds, with maxima at n = 15, 16, and 17. The peaks at m/z 262, 318, 402, etc. correspond to CnH2n-4 (tricyclic) compounds, with maxima at n = 19, 23, and 29. The peaks at m/z 372, 400, 414, etc. correspond to CnH2n-6 (tetracyclic) compounds, with maxima at n = 27, 29, and 30. The peaks at m/z 426, 454, 482, etc. correspond to CnH2n-8 (pentacyclic) compounds, with maxima at n = 31, 33, and 35. The inset of the C32 cluster peaks includes the odd-mass-numbered peaks to illustrate that cracking, which produces mainly odd-mass-numbered fragments with mass values lower than the mass of the parent molecule, does occur to a small extent. Also, a fraction of the odd-mass-numbered peaks appearing is due to the natural abundance of the 13C isotope.

Figure 4. FIMS spectra of the saturate fractions from Athabasca bitumen.

Figure 6. Z plot of the relative abundances of the tetra- and pentacyclic hydrocarbons in the saturate, subfraction 1a, as a function of the carbon number. Table 3. Gravimetric Composition of Athabasca Saturates and Approximate Composition of Cold Lake Saturates by FIMS percentage of bitumen (%)

Figure 5. Z plot of the relative abundances of the mono-, bi-, and tricyclic hydrocarbons in the saturate, subfraction 1a, as a function of the carbon number.

on Cold Lake saturates (Figure 7) illustrate at each mass number, a multitude of components are visible.6a The largest of the seven or so peaks in the m/z 318, C23 spectrum represents the most abundant member of the cheilanthane

formula

series

Cmaxa

CnH2nþ2 CnH2n CnH2n-2 CnH2n-4 CnH2n-6 CnH2n-8 CnH2n-10 total

acyclic monocyclic bicyclic tricyclic tetracyclic pentacyclic hexacyclic

19 18 15, 19 19, 23, 29 29, 27, 21, 19 30, 35, 27 40

Athabasca

Cold Lakeb

0.04 1.68 4.27 3.72 3.23 1.92 0.23 15.1

0.59 4.34 5.35 3.47 2.63 1.55 0.53 18.5

a For the Athabasca sample. b The Cold Lake sample was not distilled but was assumed to have the same concentration of non-distillables as the Athabasca sample, at 10%.

5056

Energy Fuels 2010, 24, 5053–5072

: DOI:10.1021/ef100702j

Strausz et al.

series of biomarkers, vi, present in both the Cold Lake and Athabasca saturates. Structural assignments of the peaks in Figures 2 and 3 were made on the basis of results obtained from GC and GC-MS analyses on zeolite 1310 adduction concentrates of the bi- to pentacyclic biomarker constituents of the saturates.9 These data are shown in Figures 8 and 9 and Table 4. However, before proceeding further, at this point, it may be propitious to recite the interpretation of the symbols used for the stereomeric designation of atoms or substituents in hydrocarbon molecules. For the designation of the stereomeric position of ring carbon atom-attached hydrogen atoms, a circle is used. An empty circle represents the stereomeric position below the plane of the molecule, called RH, and a filled circle represents the stereomeric position above the plane of the molecule, called βH. In the alkyl side chain, the convention of R (rectus) and S (sinister), right and left, identifying the order of arrangement of the four substituents on the asymmetric carbon, is used. The compounds denoted as bicyclic I contain a cyclic terpenoid 8β(H)-drimane ring system and an alkyl side chain

at C9 ranging in total carbon number from C15 to C24, with MS base peak at m/z 123.

Drimanes also occur in crude oils7 in functionalized forms as carboxylic acids,10 cyclic sulfides, and sulfoxides.11 In the latter two series, their carbon number extends to C31. The other bicyclic compounds listed in Table 4 had not been assigned. The compounds labeled tricyclic II are the cheilanthanes12

with the isoprenoidside chain at the C14 position up to C11, featuring a characteristic base peak in their MS at m/z 191, corresponding to the cleavage of the AB ring, and somewhat weaker signal at m/z 123, corresponding to the cleavage of the A ring.

From C25 on, the series members occur as diastereomer pairs, owing to the presence of the C22 chiral center. There are also other isomers with unidentified structures present in lesser quantities. The largest number of isomers (Figure 9), five, occurs at C19. Altogether 27 tricyclics have been detected, 16 of which belong to the tricyclic II series. The latter all headto-tail hexaprenoid triterpane series was first identified in Athabasca saturates and subsequently found to be identical with the ubiquitous tricyclic hydrocarbon biomarkers (whose structure had not been previously identified) present in all petroleums. The tricyclic II series also occur in sulfur-containing

Figure 7. FIMS scans of the C11, C14, C17, C20, C23, C26, C29, and C32 tricyclic components of the TUNA fraction.6a

Figure 8. Capillary gas chromatograms9 of the zeolite 1310 adduct fraction from Athabasca bitumen. The peak assignments are listed in Table 4.

5057

Energy Fuels 2010, 24, 5053–5072

: DOI:10.1021/ef100702j

Strausz et al.

their substrates by mild thermolysis or reductive bond cleavages. From Athabasca asphaltene, the amount of cheilanthanes generated by 300 C thermolysis exceeded the amount of cheilanthanes present naturally in saturates by about a factor of 2.5-3.0. Not surprisingly, the MW distribution of the thermally produced cheilanthanes was altered by the conversion of longer side-chain to shorter side-chain species. Pentacyclic terpenoids in saturates are represented by the ubiquitous hopane family. The hopane molecule possesses nine asymmetric carbon atoms (at the 5, 8, 9, 10, 13, 14, 17, 18, and 21 positions) and, therefore, can exist in many different isomeric forms.

Table 4. Peak Assignments for the Chromatogram Shown in Figures 8 and 9a peak number

assignement

peak number

assignement

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

C16 bicyclic C16 bicyclic C15 bicyclic C15 bicyclic C15 bicyclic, I C15 bicyclic C15 bicyclic C16 bicyclic C16 bicyclic, I CI7 bicyclic CI7 bicyclic CI8 bicyclic CI8 bicyclic CI9 bicyclic CI9 bicyclic CI9 tricyclic CI9 bicyclic CI9 tricyclic CI9 tricyclic CI9 tricyclic C20 bicyclic C20 bicyclic, I CI9 tricyclic C20 tricyclic C20 tricyclic C20 tricyclic C20 tricyclic, II C21 bicyclic, I C21 tricyclic C21 tricyclic, II C21 tricyclic C22 tricyclic, II C23 bicyclic, I C23 bicyclic, I C23 tricyclic C24 bicyclic, I C24 bicyclic, I C23 tricyclic, II C24 tricyclic, II

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

C23 tetracyclic C24 tricyclic C25 tricyclic, II C25 tricyclic, II C26 tricyclic, II C26 tricyclic, II C27 tricyclic, II C27 tricyclic, II C28 tricyclic, II C28 tricyclic, II C29 tricyclic, II C29 tricyclic, lIb C29 sterane C27 hopane C28 hopane C30 tricyclic, II C30 tricyclic, II C28 hopane C29 hopane C30 hopane-like C29 moretane C30 hopane C30 hopane-like C30 hopane-like C30 moretane C3I 22S-hopane C31 22R-hopane C31 moretane C32 22S-hopane C32 22R-hopane C32 moretane C32 moretane C33 22S-hopane C33 22R-hopane C34 22S-hopane C34 22R-hopane C3S 22S-hopane C35 22R-hopane

The stereochemistry, however, is geochemically important only at the 17 and 21 positions. In the case of extended hopanes with an alkyl side chain from C4 to C8, the C (22) position becomes asymmetric and generates more isomers. These features along with the occurrence of many hopane derivatives are then responsible for the variety of the family of hopanes in crude oil. The hopanoid and related molecules detected in Athabasca saturates are as follow:

a Plus 18R(H)-22,29,30-trisnorhopane. b A second component was also present.

crude oils in functionalized form as tetracyclic sulfides and sulfoxides,11 in which case the length of the isoprenoid side chain extends to C21, giving a total carbon number in the molecule of C40. Another significant functionalized form is the carboxylic acid derivatives with the carboxylic group at the terminal position of the isoprenoid side chain.10 Data on the absolute concentration of biomarker molecules are few and far between; nonetheless, it is generally recognized that their concentrations are low, up to a few tenths of 1%.7 Such data have, however, been obtained on the distribution of the cheilanthane family of biomarkers in the Athabasca saturates (Table 5). The total concentration in the C19-C30 range is 9.8 mg/g of saturate, and the maximum occurs at C23 > C24 > C25. Cheilanthanes, similar to other hydrocarbon-type biomarkers, in general, are also present in the bitumen in chemically bound form, attached to the asphaltenes (and to lesser extent the resins). These attached biomarkers can be liberated from (9) Dimmler, A.; Cyr, T. D.; Strausz, O. P. Org. Geochem. 1984, 7, 231–238. (10) (a) Cyr, T. D.; Strausz, O. P. Org. Geochem. 1984, 7, 127–140. (b) Cyr, T. D.; Strausz, O. P. J. Chem. Soc., Chem. Commun. 1983, 1028–1030. (11) Payzant, J. D.; Montgomery, D. S.; Strausz, O. P. Tetrahedron Lett. 1983, 24, 651–654. (12) (a) Ekweozor, C. M.; Strausz, O. P. Tetrahedron Lett. 1982, 23, 2711–2714. (b) Ekweozor, C. M.; Strausz, O. P. Advances in Organic Geochemistry; Bjoroy, M., et al., Eds.; Wiley-Heyden: Chichester, U.K., 1981; pp 746-766.

Hopanes are widely distributed in petroleum and coal. They represent one of two important classes of bio-organic molecules 5058

Energy Fuels 2010, 24, 5053–5072

: DOI:10.1021/ef100702j

Strausz et al.

Figure 9. GC-MS chromatograms9 of the zeolite 1310 fraction from Athabasca bitumen, showing the m/z 191 and 123 cross-scans. The peak assignments are listed in Table 4. Table 5. Concentration Distribution of the C19-C30 Cheilanthanes in Athabasca Saturates

formed from the same precursor, an isoprene, squalene, produced in vivo by the tail-to-tail dimerization of two C15 units. In vivo cyclization of squalene in bacteria and blue-green algae (prokaryotes) produces hopane and hopane derivatives, and in higher organisms (eukaryotes), it generates steranes and sterane derivatives. The side chains of hopanes can then subsequently be extended by bacterial processes or shortened by thermal cracking during diagenesis. Dependent upon the redox conditions of the sediment, fractions of the hopane, tetrol and cholesterol formed in series of subsequent steps, are ultimately converted in the sediments to their stable saturated hydrocarbon form. The distribution of hopanes in Athabasca bitumen saturates is depicted in Figures 2, 8, and 9, and their assignments are given in Table 4. For the illustration of their widespread occurrence, gas chromatograms of the molecular sieve 1310 adducts of Peace River core and wellhead (steamtreated) saturates,13 Grosmont bitumen and (from the same source) mineral-adsorbed asphalt saturates,14 and Lloydminster15 heavy crude oil saturates are shown in Figures 10-12 and Tables 6 and 7. As can be seen, with the exception of the Grosmont bitumen saturates (Figure 11b), the distribution of hopanes in the three deposits bears strong resemblance to one another, with minor differences reflecting variations in apparent thermal maturity, microbial degradation, water washing, and overall diagenetic history of the formations. The vast difference evident in the Grosmont bitumen samples is due to the microbial removal of the 25-CH3 group in the hopane

carbon number 19 20 21 22 23i 23 24 25 total

concentration (mg/g)

carbon number

concentration (mg/g)

0.68 0.35 0.72 0.29 0.17 2.41 1.60 1.17

26 26 27 28 28 29 29 30 30

0.23 0.43 nd 0.54 0.54 0.20 0.20 0.15 0.15 9.83 mg/g

series and consequent shifting of the base peak in the mass spectrum15 from m/z 191 to 177. If this is the case, then the m/z 177 cross-scan of the Grosmont bitumen saturates should be an imitation of the m/z 191 cross-scan15 of the hopanes. The fact that this is really the case is evident from the comparison of Figures 11 and 13. The cause of the differences between the adsorbed asphalts and the free bitumen may be attributed to the fact that the process of adsorption protects the hopanes from the microbial attack, and therefore, the regular m/z 191 cross-scan chromatogram remained unaltered. The relative proportion of the members varies with the stereomeric position of the hydrogen on C17, C21, and C22. The biological stereomer is the 17(β)21(β)22-R that, on thermal maturation, readily converts to the geometric stereomers, leading to an equilibrium distribution:

(13) McIntyre, D. D. AOSTRA Postdoctoral Fellowship Report; Department of Chemistry, University of Alberta: Edmonton, Alberta, Canada, Oct 1984. (14) Hoffmann, C. F.; Strausz, O. P. Am. Assoc. Pet. Geol. Bull. 1986, 70, 1113–1128. (15) (a) Brooks, P. W.; Fowler, M. G.; MacQueen, R. W. Org. Geochem. 1988, 12, 519–538. (b) Brooks, P. W.; Fowler, M. G.; MacQueen, R. W. Proceedings of the 4th UNITER/UNDP Conference on Heavy Crude and Tar Sands; Edmonton, Alberta, Canada, Aug 7-12, 1988.

17ðβÞ21ðRÞ22-R / 17ðRÞ21ðβÞ22-R a 17ðRÞ21ðβÞ22-S The 22-S members tend to elute before the 22-R members, and the 17(R)21(β) isomers tend to elute before the 17(β)21(R) isomers, in capillary GC DB-1 or SE-30 columns, as seen from Figure 8 and Table 4. The carbon range for the family extends 5059

Energy Fuels 2010, 24, 5053–5072

: DOI:10.1021/ef100702j

Strausz et al.

Figure 10. Gas chromatograms of the molecular sieve 1310 adducts of Peace River core and wellhead (steam-treated) saturates. B, bicyclic; T, tricyclic; H, hopane; BNH, 28,30-bisnorhopane.13 The subscripts refer to the number of carbon atoms in the molecule.

from C27 to C35 and, as seen in Figures 2 and 3, with ever decreasing concentrations to ∼C50. Hopanes represent an important class of biomarkers,7 and their distribution in Athabasca saturates indicates a mature/(early mature) status for Athabasca bitumen (vi). In connection with the quantitative aspects of the various GC-flame ionization, GC-electron impact MS, and FIMS methods of analysis, the FIMS method stands out with its ability to produce an intense ion current without significant fragmentation, resulting in a clean, easily readable, and interpretable mass distribution for the saturate. In addition, as with the paraffins, the relative ion current intensities may be assumed to be approximately independent of the MW within a structural series, and therefore, the ion current intensities measured are directly correlatable with the concentration. This latter advantageous feature of the FIMS is, at the same time, the source of its inability to yield any other information than the MW and the sum of relative concentrations of all isomeric species contributing to the observed MW. Therefore, each peak in the mass chromatogram could represent any number of different molecules with identical MW. The fact that this is indeed the case has been convincingly demonstrated by GC-FIMS studies, one example of which on the tricyclic series in Cold Lake saturates was shown in Figure 7, where at every mass number, over half a dozen component peaks can be seen. Therefore, for example, m/z 426 in Figure 3 could represent, among others, the sum of all stereomeric H31 hopanes (RβS, RβR, βRS, and βRR), and the m/z 412 peak could represent the sum of Rβ βR R and S hopanes and gammaceranes, a minor biomarker in Athabasca saturates,

again with many other pentacyclic saturated hydrocarbons with widely different structures, as long as their total ring numbers would be five. The rings would not necessarily be condensed into a single five-ring unit but could be distributed up to five units.

Now, biomarkers, such as hopanes, steranes, cheilanthanes, drimanes, etc., are all present in fossil fuels generally at low concentrations up to a few tenths of 1%. Consequently, the sum of their concentrations would not come near the 15.1 wt % of saturates in the bitumen, as determined gravimetrically (Table 2). Another interesting aspect of the FIMS mass chromatogram in Figure 3 is that the penta-, tetra-, and tricyclic peaks are all discernible far beyond the m/z 482 H35 peak, whereas in GC or GC electron impact MS determinations, the hopane series appears to terminate at C35. This feature of the FIMS spectrum appears to suggest the possibility that the limiting value in the MW of the hopane series and the tetra- and tricyclic series that has been established by GC is determined by the lack of sample volatility at the column temperature. As will be shown in the next section of this paper, H36 and H37 hopanoid compounds have been detected to be present in 5060

Energy Fuels 2010, 24, 5053–5072

: DOI:10.1021/ef100702j

Strausz et al.

small concentrations in the saturate fraction of the aqueous alkaline extract of the Athabasca oil sand. It should be noted that Alberta oil sand bitumens are typical high-sulfur bitumens, which makes it likely that the distribution of their cyclic saturates found here (Table 3 and Figures 5 and 6) would be generic to most high-sulfur bitumens. The tetracyclic complement detected in saturates features two different compound classes, the terpenoid and steroid types. The terpenoid class may appear in two isomeric forms, which are assumed to be generated by either the C17-C21 or C8-C14 bond cleavage in hopanes.

The former (17,21) C24-C27 series occurs in most oils and bitumens and has been detected in Athabasca and Grosmont carbonate bitumen14 as well. The latter (14,18) has been detected in whole Athabasca oil sands, as will be discussed in the next section of the paper. Steranes occurred in the C21-C30 range and represent the more important tetracyclic constituents of the saturates.

Figure 11. GC-MS m/z 191 cross-scan chromatograms, showing the tricyclic terpanes and hopanes in (a) Athabasca, (b) Grosmont, and (c) Grosmont-B (bound) oil sand bitumens.14 The peak assignments are listed in Table 6.

bound steranes contain only regular steranes.16 For carbon number distribution of the degraded steranes in the bitumen, the order is C27>C28>C29, but for the undegraded steranes in the asphaltene, the carbon number distribution is C29 > C27>C28. A comparison of the m/z 217.2 cross-scans of the Athabasca and Grosmont bitumen saturates, on the one hand, to those of the Peace River bitumen saturates and Lloydminster heavy oil saturates, (Figure 15 and Table 9), on the other hand, reveals a significant presence of regular steranes in the latter two materials and, thus, a less severe biodegradative state for them. Thus, from these results, it can be concluded that the severity of biodegradation follows the order Grosmont ≈ Athabasca > Peace River > Lloydminster. According to literature reports,15 the most severely biodegraded bitumens in the western Canada sedimentary basin occur in some

The biologically derived cholestane possesses eight asymmetric centers, of which only the C-5, C-14, C-17 and C-20 members are geochemically important, which then generate many isomers. The distribution of steranes in the Athabasca saturates in comparison to the Grosmont saturates and mineral-bound saturates is shown in Figure 14 and Table 8. Steranes are microbiologically readily degradable molecules, and upon maturation in their host sediments, they can be thermo-catalytically decomposed or converted to their isomers, the diasteranes, which are thermally and microbiologically more stable than the regular steranes. As a result, in thermally mature microbiologically heavily downgraded bitumens, such as the Athabasca and Grosmont bitumens,14,15 of which the characteristic m/z 217.2 cross-scan GC-MS is shown in Figures 14 and 15 and Table 9, most of the steranes are present in the diasteranes form, but in the adsorbed fraction of the Grosmont bitumen, uppermost panel of Figure 14, the regular steranes dominate and the Athabasca asphaltene-

(16) Peng, P.; Morales-Izquierdo, A.; Hogg, A.; Strausz, O. P. Energy Fuels 1997, 11, 1171–1187.

5061

Energy Fuels 2010, 24, 5053–5072

: DOI:10.1021/ef100702j

Strausz et al.

Figure 12. GC-MS m/z 191 cross-scan chromatograms, showing the tri- and pentayclic terpane distribution in Lloydminster, Athabasca, Peace River, and Grosmont heavy oils and bitumens.15 The peak assignments are listed in Table 7. Reprinted with permission from Elsevier Science Ltd. Table 6. Structural Assignments of the Peaks in Figure 11a compound A B C D D-1 D-2,3

C28 tricyclic terpane (22S þ R) C29 tricyclic terpane (22S þ R) 18R(H)-22,29,30-trisnorneohopane 17R(H)-22,29,30-trisnorhopane 17R(H),21β(H)-29,30-bisnorhopane C30 tricyclic terpane (22S þ R)

C28H52 C29H54 C27H46 C27H46 C28H48 C30H56

D-4

17R(H),21β(H)-28,30-bisnorhopane þ 17β[(H),21R(H)-28,30-bisnorhopane

C28H48

E F G H I J K L M

17R(H),21β(H)-30-norhopane 17β[(H),21R(H)-30-norhopane 17R(H),21β(H)-hopane 17β[(H),21R(H)-hopane 17R(H),21β(H)-homohopanec 17R(H),21β(H)-bishomohopanec 17R(H),21β(H)-trishomohopanec 17R(H),21β[(H)-tetrakishomohopanec 17R(H),21β[(H)-pentakishomohopanec

C29H50 C29H50 C30H52 C30H52 C31H54 C32H56 C33H58 C34H60 C35H62

a

structureb

elemental composition

From ref 14. b

c

I I II III III I IVa IVb III V III V III III III III III

R0 = CH3, R00 = C9H19 R0 = CH3, R00 = C10H21 R* = H R* = H R* = CH3 R0 = CH3 R00 = C10H21 R* = C2H5 R* = C2H5 R* = CH(CH3)2 R* = CH(CH3)2 R* = CH(CH3)C2H5 R* = CH(CH3)C3H7 R* = CH(CH3)C4H9 R* = CH(CH3)C5H11 R* = CH(CH3)C6H13

22S þ R.

Table 7. Compounds Identified in the m/z 191 Fragmentograms Shown in Figures 12 and 13 and Also for the m/z 177 in Figure 13 peak

compound

peak

compound

A B C D E F G H I J K L M

C23 tricyclic terpane C24 tricyclic terpane C25 tricyclic terpane C24 tetracyclic terpane C26 tricyclic terpane isomers C28 tricyclic terpane isomers C29 tricyclic terpane isomers 18R(H)-trisnorhopane (Ts) 17R(H)-trisnorhopane (Tm) 28,30-bisnorhopanes 17R(H),21β(H)-norhopane 17R(H),21β(H)-hopane 17β(H),21R(H)-moretane

N 0 P Q R S T U V W X Y Z

17R(H),21β(H)-homohopanes (20S þ 20R) gammacerane 17R(H),21β(H)-bishomohopanes (20S þ 20R) 17R(H),21β(H)-C33 hopanes (20S þ 20R) 17a(H),21β(H)-C34 hopanes (20S þ 20R) 17a(H),21β(H)-C35 hopanes (20S þ 20R) 17R(H)-25-norhopane 17R(H)-25,30-bisnorhopane 17R(H)-25-norhomohopanes 17R(H)-25-norbishomohopanes 17R(H)-25-nor-C32 hopanes 17R(H)-25-nor-C33 hopanes 17R(H)-25-nor-C34 hopanes

5062

Energy Fuels 2010, 24, 5053–5072

: DOI:10.1021/ef100702j

Strausz et al.

Figure 13. GC-MS m/z 191 and 177 cross-scan chromatograms, showing the tri- and pentacyclic terpane distribution in a carbonate triangle oil sand bitumen, Grosmont.15 The peak assignments are listed in Table 7. Reprinted with permission from Elsevier Science Ltd.

Grosmont and Nisku formation deposits, from which even the diasteranes have been removed. The C21-C22 steranes occur in significant concentration in the saturates of all of the bitumens and heavy oils (Figures 14-16), only in the regular form, regardless of their biodegradative status; these low-MW steranes are highly resistant against biodegradation. Hexacyclics occur at low concentrations, as seen from the FIMS spectrum (Figure 3), in front of the m/z 412, 426, 440, 454, 468, 482, etc. peaks of the hopane series. Their structures have not been determined. However, because benzohopanes ranging from C32 to C35 have been detected in the monoaromatic subfraction of the aqueous alkaline extract of the bitumen, it is reasonable to assume that the precursors of the benzohopanes in the sediment would also be present.

Their carbon range, similar to the penta- and tetracyclic alkanes, appears to extend to or even beyond C45, with a maximum around C40.

Additional contribution to the hexacyclic series17 may come from the hexacyclic isoprenoid series identified18 in extracts of Upper Cretaceous sediments and perhaps from the

Figure 14. GC-MS m/z 217.2 cross-scan chromatograms, showing the C27-C29 steranes in Athabasca and Grosmont (B = bound) bitumens.14 The assignments of peaks e-x are listed in Table 8.

(17) Peters, K. E.; Walters, C. C.; Moldowan, J. M. The Biomarker Guide, 2nd ed.; Cambridge University Press: Cambridge, U.K., 2007. (18) Schaeffer, P.; Poinsot, J.; Hauke, V.; Adam, P.; Wehrung, P.; Trendel, J. M.; Albrecht, P.; Dessort, D.; Connan, J. Angew. Chem., Int. Ed. 1994, 33, 1166–1169.

hexacyclic C34 compounds, which were found to be abundant inextracts from the Lower Cretaceous Ostracode Zone in 5063

Energy Fuels 2010, 24, 5053–5072

: DOI:10.1021/ef100702j

Strausz et al.

Table 8. List of Steranes Identified in Athabasca and Grosmont Saturates Shown in Figure 14

carbons as the carbon framework of the bicyclic sulfides11,20-24 and sulfoxides11,20-24 also occur in the saturate fraction of the bitumen.

southern Alberta.19

Adamantane and its methyl, propyl, and butyl derivatives detected in Peace River bitumen and Lloydminster13 heavy oil Monocyclic alkanes are present in the C13-C35 range, with a maximum at C18. Their structures were not investigated, but as with the hexacyclics, strong inference suggests that, in accordance with the tri-, tetra-, and hexacyclic sulfides and sulfoxides where the cyclic terpenoid carbon frameworks, the drimanes, cheilanthanes, and hopanes appear in the saturates as the free hydrocarbons and the monocyclic terpenoid hydro-

(20) (a) Payzant, J. D.; Cyr, T. D.; Montgomery, D. S.; Strausz, O. P. Tetrahedron Lett. 1985, 26, 4175–4178. (b) Payzant, J. D.; Cyr, T. D.; Montgomery, D. S.; Strausz, O. P. In Geochemical Biomarkers; Yen, T. F., Moldowan, J. M., Eds.; Hardwood Academic: Chur, Switzerland, 1988, p 133. (21) Payzant, J. D.; Montgomery, D. S.; Strausz, O. P. Org. Geochem. 1986, 9, 357–369. (22) Peng, P. P.; Morales-Izquierdo, A.; Fu, J.; Sheng, G.; Jiang, J.; Hogg, A.; Strausz, O. P. Org. Geochem. 1998, 28, 125–134. (23) Cyr, T. D.; Payzant, J. D.; Montgomery, D. S.; Strausz, O. P. Org. Geochem. 1986, 9, 139–143. (24) Strausz, O. P.; Lown, E. M.; Payzant, J. D. In Geochemsitry of Sulfur in Fossil Fuels; Orr, W. L., White, C. M., Eds.; American Chemical Society: Washington, D.C., 1990; ACS Symposium Series 429, pp 83-92.

(19) Riediger, C. L.; Fowler, M. G.; Snowdon, L. R. In Petroleum Geology of the Cretaceous Mannville Group, Western Canada; Pemberton, S. G., James, D. P., Eds.; Canadian Society of Petroleum Geologists: Calgary, Alberta, Canada, 1997; pp 93-102.

5064

Energy Fuels 2010, 24, 5053–5072

: DOI:10.1021/ef100702j

Strausz et al.

Figure 15. GC-MS m/z 271.2 cross-scan chromatograms, showing the sterane distributions in Lloydminster heavy oil and Athabasca, Peace River, and Grosmont oil sand bitumens.15 The peak assignments are listed in Table 9 ª1988 Elsevier Science Ltd. Table 9. Compounds Identified in the m/z 217.2 Fragmentograms Shown in Figure 15 peak

compound

1 2 3 4 5 6

C21 sterane C22 sterane 13β(H),17β(H)-diacholestane (20S) 13β(H),17R(H)-diacholestane (20R) 5R(H),14R(H),17R(H)-cholestane (20S) 5R(H),14β(H),17β(H)-cholestane (20R) þ 24-ethyl-13β(H),17R(H)-diacholestane (20S) 5R(H),14β(H),17β(H)-cholestane (20S) 5R(H),14R(H),17R(H)-cholestane (20R) 24-ethyl-13β(H),17R(H)-diacholestane (20R) 24-methyl-5R(H),14R(H),17R(H)-cholestane (20R) 24-ethyl-5R(H),14R(H),17R(H)-cholestane (20S) 24-ethyl-5R(H),14β(H),17β(H)-cholestane (20R) 24-ethyl-5R(H),14β(H),17β(H)-cholestane (20S) 24-ethyl-5R(H),14R(H),17R(H)-cholestane (20R)

7 8 9 10 11 12 13 14

were not detected in Athabasca saturates.

In another, novel approach to the investigation of the biomarker constituents of the bitumen, the whole oil sands were extracted with dilute aqueous base. This method offers the advantage of ease, speed, and simplicity while opening a new window on biomarker content, rendering the detection of additional species possible. Typically, about 300 g of oil sands were extracted with 600 mL of 0.01 M aqueous NaOH at temperatures between 80 C and the reflux temperature of the aqueous slurry from 10 min to 48 h in duration. The tri- and pentacyclic terpenoid hydrocarbons are clearly evident in the GC-MS m/z 191 cross-scan of the saturated

Figure 16. GC-MS m/z 217.2 cross-scan chromatograms, showing the C21-C22 steranes in Athabasca and Grosmont bitumens.14 The structures of peaks a-d are listed in Table 8.

hydrocarbon fraction of the extract, shown in Figure 17. This similarity of the tri- and pentacyclic terpenoid distributions to their analogues in the saturates (Figures 9-12) is clearly 5065

Energy Fuels 2010, 24, 5053–5072

: DOI:10.1021/ef100702j

Strausz et al.

Figure 17. GC-MS m/z 191 cross-scan of the aqueous extract of Athabasca oil sands, showing the distribution of the tri- and pentacyclic terpenoid hydrocarbons from the extraction of 300 g of oil sands plus 0.5 g of NaOH with 600 mL of water for 48 h.

Figure 18. Enlargement of the 45-54 min portion of the GC-MS m/z 191 cross-scan of Figure 17, showing the C36 and C37 hopane isomers in the alkaline process water.

along with a C27-C31 series of 8,14-secohopanes, each involving many different isomers (Figures 20-24). Shown in the figures are the parent ion cross-chromatograms, m/z 372, 386, 400, 414, and 428, for the C27-C31 members together with the mass spectrum of a select, representative species of the series. Steranes were also detected in the extract in a similar distribution as in the Athabasca and Grosmont bitumens (Figure 25). The series is dominated by the regular steranes at C21-C22 and the diasteranes from C27 upward. Bicyclics were represented by a short series from C16 to C19 and two mono-unsaturated bicyclics of C19. Acyclics present in the bitumen are estimated to be around 0.04%. The only members of them detected were a short series

evident, with the exception of the presence of trace quantities of C36 and C37 hopanoids (Figures 18 and 19), each of which features three isomers. These species have not been seen in Athabasca bitumen before, although C36 and C37 extended hopanes25 and C36-C40 hopanes have been reported in the literature.26 The species at retention times of 46.4, 48.2, 50.3, and 52.4 min appear to be the two extended members of the R and S epimeric homohopane series. Additional hopanoids detected here but not in the bitumen are C32-C35 benzohopanes and some hopenes, C27, C30, and C31, (25) Grice, K.; Schaeffer, Ph.; Schwark, L.; Maxwell, J. R. Org. Geochem. 1996, 25, 131–147. (26) Rullk€ otter, J.; Philip, P. Nature 1981, 292, 616–618.

5066

Energy Fuels 2010, 24, 5053–5072

: DOI:10.1021/ef100702j

Strausz et al.

Figure 19. EIMS of the C36 and C37 hopanes in the Figure 17 extract.

of n-alkanes up to ca. C36 (Figure 26), a portion of which appears to be also present as adsorbates associated with the mineral matter via the agency of chemisorbed carboxylic acids and humic materials (Figure 27). The lower MW portion of the series if present, which is likely the case, would have been lost in the recovery process. Low-MW, C1-C7 hydrocarbons along with dissolved gases and volatiles, such as CO, CO2, COS, H2S, acetaldehyde, etc., can be separated from whole oil sands upon degassing.3 Their presence is a clear manifestation of the currently ongoing microbiological processes in the oil sands reservoirs. Indeed, a significant population of dormant bacteria (and other organisms) down to a depth of 700 m has been detected in Athabasca deposits.27

quite large for the non-distillable subfraction, indicating the presence of fairly long alkyl chains. In the aromatic region (110-150 ppm), the NMR spectrum indicates trace amounts of aromatic carbon in the distillable saturate subfraction and low but more than a trace level of aromatic carbon in the non-distillable subfraction. In effect, the NMR spectrum of the non-distillable subfraction bears a fairly close resemblance to that of the asphaltene.3 General Considerations The present paper sets forth a fairly complete outline of the chemical composition of the Athabasca oil sand bitumen saturate fraction along with a detailed analytical outline for the quantitative isolation of pure saturates. It is shown that, after column chromatographic separation, it is necessary to subject the crude saturate to molecular distillation and silver ion chromatographic separation (Figure 1 and Table 1). The rest of the maltene was eluted with various solvents, with each fraction distilled yielding 14 fractions of distilled and 14 fractions of non-distillable aromatics and resins, of which the analytical results will be reported in forthcoming papers. The purified saturate is shown by its FIMS spectrum (Figure 3), to be comprised of mono- to pentacyclic saturated hydrocarbons with low levels of hexacyclics and trace quantities of acyclics. For the illustration of the efficacy of the fractionation method employed, the FIMS chromatogram of the saturates obtained by the saturates, aromatics, resins, and asphaltenes (SARA) method is also presented in Figure 4. In this case, the sulfur, aromatic, and asphaltene-like compounds blur the characteristic pulsed MW distribution of the pure saturates seen in Figure 3 that makes the mass spectrogram so revealing.

Non-distillables Returning to the molecular distillation of fraction 1 (Figure 1), the distillables and non-distillables may differ in molecular size, chemical composition, or both. Indeed, fundamental and characteristic differences in the chemical composition are revealed by the 13C nuclear magnetic resonance (NMR) spectrum28 (Figures 28 and 29) in the aliphatic (10-60 ppm) portion of the distillable subfraction, indicating a low (less than unity) ratio for the midchain methylene (peak 7) over the chain end methyl (peaks 1) resonance, manifesting the absence of long alkyl chains in the distillable saturate subfraction. On the contrary, the value for this ratio is (27) Weslake, D. W. Private communication; University of Alberta, Edmonton, Alberta, Canada, 1978. (28) Mojeslky, T. W. AOSTRA Fellowship Report; University of Alberta: Edmonton, Alberta, Canada, 1992.

5067

Energy Fuels 2010, 24, 5053–5072

: DOI:10.1021/ef100702j

Strausz et al.

Figure 20. GC-MS m/z 372 cross-scan of the Figure 17 extract and the mass spectrum of scan 941.

tion of maltene and asphaltene. As discussed before29 in the n-pentane (or n-heptane) precipitation of asphaltene from a methylene chloride solution of the bitumen, some polar aromatic components of the maltene, through an adsorptive equipartitioning between the solution phase and the solid precipitate, co-precipitate with the asphaltene. The co-precipitated resin molecules can be removed from the asphaltene by several dissolution-reprecipitation cycles. At the same time, some of the low-MW asphaltene components, the non-distillable asphaltene-like fractions present in all fractions of the maltene, remain in solution in the solvent, precipitant (CH2Cl2/ n-C5H12) solvent. Increasing the solvent power by shifting to n-heptane will reduce the co-precipitated resins but, at the same time, will increase the amount of the low-MW asphaltene left in the solution phase that is in the maltene. In about 40% of the maltene, the non-distillables may comprise as much as 50% of the parent maltene (Figure 1). If the nondistillables were collected from the whole maltene, it is likely that a significant portion of them would precipitate under standard conditions as asphaltene. As was mentioned above, there is a large discrepancy between the ring number distribution in the molecules of the saturates as determined from the FIMS spectrum (Figure 3 and Table 3) and the biomarker distribution from capillary GC or GC-MS spectra (Figures 2, 8-10, and 12). Thus, for example, the highest concentration of biomarkers present from the gas chromatograms appears to be that of the hopanes,

Figure 21. GC-MS m/z 386 cross-scan of the Figure 17 extract and the mass spectrum of scan 972.

The occurrence of the non-distillable asphaltene-like material in the saturate fraction is a manifestation of the inherent fuzziness of the solvent precipitation method for the separa(29) Strausz, O. P.; Torres, M.; Lown, E. M.; Safarik, I.; Murgich, J. Energy Fuels 2006, 20, 2013–2021.

5068

Energy Fuels 2010, 24, 5053–5072

: DOI:10.1021/ef100702j

Strausz et al.

Figure 22. GC-MS m/z 400 cross-scan of the Figure 17 extract and the mass spectrum of scan 986.

Figure 23. GC-MS m/z 414 cross-scan of the Figure 17 extract and the mass spectrum of scan 1016.

Figure 24. GC-MS m/z 428 cross-scan of the Figure 17 extract and the mass spectrum of scan 1048.

whereas from the FIMS chromatogram (Figure 3), the highest concentration of biomarkers present appears to be that of the bicyclics. Also, the total concentration of detected biomolecules is estimated to be only a few percentages of saturates (cf. Table 5); these are clear indications that the bulk of saturates, as expected, is comprised of yet unidentified molecules. To gain more insight into the molecular nature of the bulk constituents in greater detail, it will be instructive to briefly examine at this point the distribution of the FIMS-measured MW (Figures 5 and 6) of the bulk saturates and the GC-MS fragment ion cross-scan determined MW distribution of the biomarkers (Figures 9, 10, and 14), to assess the extent of a possible correlation between them. This will be performed below for each ring-number compound class separately. Pentacyclics. In both materials, the major maximum occurs at C30, with minor maxima at C27 and C35. Therefore, it is reasonable to conclude that the bulk of the pentacyclics,

1.9% of the bitumen, is closely related to the hopane family. This is about 1 order of magnitude higher than the estimated total concentration of the 17R(H)-hopanes in crude oils, ∼2000 ppm.7 Tetracyclics. Here again, the correlation between the bulk and the sum of the steranes þ secophanes distribution is very good. The major maximum in both materials occurs at ∼C29, with minor maxima at C19, C21, and C35. Therefore, the chemical nature of the bulk, 3.23% tetracyclics, should be closely similar to that of the assumed ∼2000 ppm7 sterane biomarkers in saturates. Tricyclics. The correlation again is quite convincing. The major maximum occurs in both materials at C19, with minor ones at C23 and C29. The tricyclic content measured was 3.72% in the bulk, and the cheilanthane content was ∼0.2%. Bi- and Monocyclics. In these cases, the biomarker structure is not well-established. The B15 could arise from T19, and B16 5069

Energy Fuels 2010, 24, 5053–5072

: DOI:10.1021/ef100702j

Strausz et al.

Figure 25. GC-MS m/z 217 cross-scan of the Figure 17 extract, showing the distribution of steranes.

Figure 26. GC-MS m/z 57 cross-scan of the nonpolar fraction from the extraction of 300 g of oil sands with 600 mL of 0.01 M aqueous NaOH at 80 C for 10 min, showing n-alkanes.

Figure 27. GC-MS total ion current chromatogram of CH2Cl2 Soxhlet-extracted oil sands (300 g) treated with 0.01 M NaOH for 15 min at 80 C, showing the C22-C30 n-alkanes.

could arise from T20 or the carbon skeleton of the tricyclic terpenoid sulfide. A microbiological origin and an oxidation process of the unsaturated hopanetetrol has been suggested.5,7,30,31 In any event, there are several different isomers present mainly in the C15-C24 range in a total amount of

4.27% of saturates. Monocyclics could arise from the ring opening of drimanes or the bicyclic terpenoid sulfide skeleton. The monocyclic complement of the Athabasca saturates is 1.63%, but in the Cold Lake saturates, their concentration is much higher, at 4.34%. Saturates of the microbiologically less degraded Cold Lake bitumen have also been investigated. In this case, the FIMS instrument was coupled to a GC instrument. Figure 7

(30) Alexander, R.; Kagi, R.; Noble, R. A. J. Chem. Soc., Chem. Commun. 1983, 226–228. (31) Noble, R. A.; Alexander, R. Prepr.—Am. Chem. Soc., Div. Pet. Chem. 1989, 138.

5070

Energy Fuels 2010, 24, 5053–5072

: DOI:10.1021/ef100702j

Strausz et al.

Figure 28. Inverse-gated decoupled 13C NMR spectrum (500 MHz) of the non-distillable (240 C, 10-3 Torr) portion of Athabasca saturates.

Figure 29. Inverse-gated decoupled 13C NMR spectrum (500 MHz) of the distillable (240 C, 10-3 Torr) portion of Athabasca saturates.

chromatogram of Figure 2 and peak 38 of Figures 8 and 9. The area under this peak represents only a fraction of the total C23 area. The chromatograms in Figure 7 also provide useful hints regarding the mode of condensation in the ring structures of these molecules. The single unimodal humps superposed by sharp peaks progressively shifting to longer elution times with increasing carbon number strongly suggest that the CnH2n-4 molecular frameworks are indeed

is an illustration of a GC-FIMS chromatogram, showing the distribution of the tricyclic components of the TUNA fraction of Cold Lake saturates. For the sake of clarity, only every third member of the series is being displayed. As evident, there are numerous different compounds present at every carbon number, of which only one or two would be known as biomarkers. The sharp, large peak at C23 is the major component of the alkyl cheilanthanes, T23 in the GC 5071

Energy Fuels 2010, 24, 5053–5072

: DOI:10.1021/ef100702j

Strausz et al. 12

representing single, triply condensed naphthenic rings, isomers of the cheilanthanes (without significant contributions by a double condensed plus a mono-aromatic or three monoaromatics molecular framework), which could possibly be genetically related to cheilanthanes. Upon a comparison of the data to those of the Athabasca bitumen saturates, it is seen that the total saturate content is 18.5% of the bitumen in the Cold Lake versus 15.1% in the Athabasca sample. Also, the relative concentration of the Cold Lake saturates is shifted to lower ring numbers, but their order remains nearly the same. In addition, there are more acyclics and hexacyclics in the Cold Lake than the Athabasca sample. Unlike in the Athabasca sample, the Cold Lake saturates were found to contain a series of acyclic isoprenes in the C19-C40 range, including pristane and phytane. All of these features support the lesser degree of biodegradation in the Cold Lake deposit. Lastly, a word about the interpretation of biomarkers with respect to the origin, depositional environment, source rock, microbiological, and diagenetic history of the bitumen. It is to be noted that the saturated hydrocarbon-type biomarkers identified in the saturate fraction of the oil, in general, do not give a complete account of the past history of the bitumen. The biomarker molecules may undergo thermo-catalytic, reductive, oxidative microbiological, etc. alterations in the source and reservoir rocks. It has been discovered32 over 30 years ago that asphaltene also contains hydrocarbon-type biomarkers chemically bound to the asphaltene molecule, which can be liberated by mild thermolysis. Shortly afterward, it was also discovered that other compound class fractions of the bitumen or oil, the aromatics, polars, or resins also contain chemically bound hydrocarbon-type biomarkers12 and that these biomarkers may exist in functionalized33,34 forms as well. The bound biomarkers have distributions corresponding to a younger, earlier age of the sediments, owing to the protective effect of their molecular environment from contact with catalysts, microbes, oxygen, water, etc. (an example is the production of cheilanthanes, hopanes, etc. by the mild thermolysis of

Athabasca resins ). Alternatively, hydrocarbon-type biomarkers can be liberated by chemical treatment of the host molecules16 (e.g., NiB reduction or BBr3 cleavage of ether or ester C-O bonds in asphaltenes). In the Ru ions, catalyzed oxidation of asphaltene hydrocarbon-bound biomarker appendages are liberated33 as their carboxylic acid derivatives, etc. A spectacular example of the effect of functionalization is the hexacyclic hopanoid sulfides and sulfoxides isolated from Athabasca resins.34 In this case, reduction of the sulfides/sulfoxides yielded hopanes, in which the 22-R biological epimer is more abundant than the 22-S geological epimer and the H35 member may be the most abundant member of the series.34 Yet, another example is the case of sterane distribution in Athabasca saturates, where the dominant form of steranes is the diasterane isomer and regular steranes in the C27-C30 range are present at very low concentrations. In the asphaltene-bound states, however, all steranes exist in the regular form.16 Therefore, a more complete discussion of the interpretation of biomarkers will be postponed until the publication of the forthcoming parts of this series on the chemistry of Athabasca bitumen. Nonetheless, the biomarkers that have been encountered thus far in the present paper are consistent with and, therefore, lend support to the notion that Athabasca bitumen is the residue of the secondary microbiological degradation of mature/(early mature) marine carbonate oils, formed in a strongly reducing depositional environment, as will be shown at a later date. Some of the macroscopic characteristics of the bitumen, for example, the high sulfur35 (5.0%) and thiophenic sulfur content,36 along with high vanadium concentrations (∼190 ppm) and V/(V þ Ni) ratios37 (∼0.72) and low API gravity38 (8-10), give additional support for this conclusion. (35) Strausz, O. P.; Rubinstein, I.; Hogg, A. M.; Payzant, J. D. In Atomic and Molecular Methods in Fossil Energy Research; Filby, R. H., Carpenter, B. S., Ragaini, R. C., Eds.; Plenum: New York, 1982; pp 409-441. (36) (a) Payzant, J. D.; Lown, E. M.; Strausz, O. P. Energy Fuels 1991, 5, 445–453. (b) Payzant, J. D.; Mojelsky, T. W.; Strausz, O. P. Energy Fuels 1989, 3, 449–454. (c) Payzant, J. D.; Montgomery, D. S.; Strausz, O. P. AOSTRA J. Res. 1988, 4, 117–131. (d) Payzant, J. D.; Rubinstein, I.; Hogg, A. M.; Strausz, O. P. Geochim. Cosmochim. Acta 1979, 43, 1187–1193. (37) Filby, R. H.; Strong, D. In Tar Sand and Oil Upgrading Technology; Shih, S. S., Oballa, M. C., Eds.; American Institute of Chemical Engineers (AIChE): New York, 1991; AIChE Symposium Series 282, Vol. 87, p 1. (38) 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 177-189.

(32) Rubinstein, I.; Spyckerelle, C.; Strausz, O. P. Geochim. Cosmochim. Acta 1979, 41, 1–6. (33) (a) Strausz, O. P.; Mojelsky, T. W.; Faraji, F.; Lown, E. M.; Peng, P. Energy Fuels 1999, 13, 207–227. (b) Peng, P.; Fu, J.; Sheng, G.; MoralesIzquierdo, A.; Lown, E. M.; Strausz, O. P. Energy Fuels 1999, 13, 266–277. (34) Cyr, T. D. AOSTRA Fellowship Report; University of Alberta: Edmonton, Alberta, Canada, Oct 1983.

5072