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Energy & Fuels 1998, 12, 262-267
Reduction of Molecular Motion of Polymethylene in Oil Shales by Mineral Matter Garry S. H. Lee,*,† Adam J. Berkovich,† John H. Levy,‡ Brent R. Young,† and Michael A. Wilson† Department of Chemistry, University of Technology, Sydney, P.O. Box 123, Broadway NSW 2007, Australia, and Division of Coal and Energy Technology, Commonwealth Scientific and Industrial Research Organisation, Menai NSW, Australia Received June 16, 1997. Revised Manuscript Received November 24, 1997
Kerogen from the Stuart deposit, Queensland, Australia has been isolated from its oil shale by a number of methods and studied by solid-state 13C nuclear magnetic resonance spectroscopy (NMR). The kerogen is unusual, since there is clear evidence of a resolved polymethylene peak in the NMR spectrum rather than the broad resonance at about the same chemical shift normally obtained for highly aliphatic kerogens with aromaticities less than 0.25. X-ray diffraction data also indicate some ordered material in the kerogen. This polymethylene peak is not present in the NMR spectrum of the original oil shale and is absent in spectra of both oil shales and kerogens of similar deposits (e.g., Condor, Queensland, Australia). The mineral-matter components of Stuart oil shale do not differ significantly from oil shales with conventional kerogen NMR spectra. It may be concluded that precursor biopolymers in Stuart kerogen are not as cross-linked as other aliphatic kerogens such as Condor. This could be due to a higher concentration of Pediastrum species in the kerogen-forming biomass.
Introduction Kerogen composition determines oil yield in natural and man-made processes of petroleum formation, yet our knowledge of kerogen chemical structure is limited. A recent review summarizes current knowledge.1 One recent major advance has been the appreciation that insoluble aliphatic macromolecular components of many algae2,3 are the building blocks of kerogen, for example, Botrycoccocenes brauni. Both branched-chain and linear alkadienes have been identified in residues depending on race3-9 and may be found in polymerized and monomer forms. The insoluble macromolecular components of algae are preferentially preserved rather than degraded10 during the kerogen-forming process. The preserved * To whom correspondence should be addressed. † University of Technology, Sydney. ‡ Commonwealth Scientific and Industrial Research Organisation. (1) Engel, M. H.; Macko, S. A. Organic Geochemistry Principles and Applications; Plenum Press: London, 1993. (2) Gelin, F.; de Leeuw, J. W.; Sinninghe, D.; Jaap, S.; Derenne, S.; Largeau, C.; Metger, P. Org. Geochem. 1994, 21, 432. (3) Maxwell, J. R.; Douglas, A. G.; Eglington, G.; McCormick, A. Phytochemistry 1968, 7, 2157. (4) Metzger, P.; Casaderall, E.; Pouet, M. J.; Pouet, Y. Phytochemistry 1985, 24, 2995. (5) Metzger, P.; Berkaloff, C.; Casaderall, E.; Coute, A. Phytochemistry 1985, 24, 2305. (6) Wake, L. V.; Hillen, L. W. Aust J. Mar. Freshwater Res. 1981, 32, 353. (7) Brown, A. C.; Knights, B. A.; Conway, E. Phytochemistry 1969, 8, 543. (8) Galbraith, M. N.; Hillen, L. W.; Wake, L. V. Phytochemistry 1983, 22, 1441. (9) Knights, B. A.; Brown, A. C.; Conway, E.; Middleditch, B. S. Phytochemistry 1970, 9, 1317. (10) Hatcher, P. G.; Spiker, E. C.; Szeverenyi, N. M.; Maciel, G. E. Nature 1983, 305, 498.
material may be modified by cross-linking, by the effects of thermal maturation, or through deposition of organic material of terrestrial, lacustrine, or deltaic origin.11,12 Little is known of the cross-linking in these algally derived macromolecules, even before thermal maturation. However, it has been demonstrated that, after stepwise oxidation of kerogens, the distribution of normal monocarboxylic and R,ω-dicarboxylic acids indicates that the number of cross-linked polymethylene bridges are in the range C10-C12 for some highly aliphatic kerogens.11 This is consistent with crosslinking of alkadienes with double bonds every 10-12 carbons to form tertiary carbons. As noted above, alkadienes of this type are found in colonies of Botryococcus brauni, and it is plausible that many algae could form such structures. It seems probable that sulfur or alcoholic groups may also be involved in cross-linking, particularly as kerogens mature.13 Kerogens are normally isolated from inorganic matrixes, and hence, bonding with the matrix is possible. Clays are often suggested as likely candidates; however, it is not clear how they may bond. There is also the possibility that the kerogen is physically trapped between the aluminosilicate plates. It is clear that kerogens are still insoluble once the clay matrix is removed so that there is little direct evidence for clay-kerogen interactions. On the basis of organic model compound studies, it seems that acid-base interactions are important,14 but the evidence is not convincing unless (11) Barakat, A.; Yen, Y. F. Energy Fuels 1988, 2, 181. (12) Mann, A. L.; Patience, R. L.; Poplett, I. J. F. Geochim. Cosmochim. Acta 1991, 55, 2259. (13) Patience, R. L.; Mann, A. L.; Poplett, I. J. F. Geochim. Cosmochim. Acta 1992, 56, 2725.
S0887-0624(97)00087-X CCC: $15.00 © 1998 American Chemical Society Published on Web 01/24/1998
Polymethylene in Oil Shales
substantial amounts of nitrogen bases can be observed in oil shales, which is not the case here (see below). Another possibility is bonding through the host of silicate species in various polymer and equilibrating forms present in aqueous solutions of silicic acid.15-21 A number of techniques have been used to characterize oil shales, other petroleum-source rocks, and kerogens. Over the past 20 years solid-state 13C NMR has become the method of choice because it can be used to determine the fraction of carbon that is aromatic, fa, and the analysis is now routine, although there is considerable debate concerning quantitation.21 Nevertheless, there are few comparative studies of both oil shale and kerogen, prepared by demineralization, possibly because the limited studies show little difference between oil shale and kerogen spectra.21-23 During a study of the process by which oil is formed during rotary kiln pyrolysis of oil shale from the Stuart deposit in Queensland, Australia, we noticed differences in 13C-NMR spectra between kerogen and oil shale that identify clear structural changes during isolation. These findings are reported here along with comparative studies of other oil shales. The results are interpreted in terms of degree of polymerization of the polymer macromolecules before kerogen isolation. Experimental Section This study concentrates on oil shales from the Stuart deposit, Queensland, Australia, but other Tertiary oil shales from the Condor deposit in Queensland and Tasmanite from Tasmania have been included for comparison. Details of these oil shales are given elsewhere.24-33 Mineralogy of the Stuart and Condor oil shales determined by X-ray diffraction (see below) is shown in Table 1. The Stuart deposit, which is contiguous to the Rundle deposit, is located in The Narrows Graben, near Gladstone, whereas the Condor deposit is located further north around Bowen. The oil shales were formed in brackish to freshwater lakes colonized by planktonic algae such as Pediastrum. Pediastrum is present in differing (14) Siskin, M.; Payack, M. Energy Fuels 1987, 1, 248. (15) Williams, E. A.; Cargioli, J. D. Annual Reports on NMR Spectroscopy; Webb, G. A., Ed.; Academic Press: London, 1979. (16) Alvarez, R.; Sparks, D. L. Nature 1985, 318, 649. (17) Harris, R. K.; Knight, C. T. G.; Hull, W. E. J. Am. Chem. Soc. 1981, 103, 1577. (18) Cary, L. W.; de Jong, B. H.; Dibble, W. E., Jr. Geochim. Cosmochim Acta 1982, 46, 1317. (19) Iler, R. K. The Chemistry of Silica; Wiley: New York, 1979. (20) Harris, R. K.; O’Connor, M. J.; Curzon, E. H.; Howarth, O. W. J. Magn. Reson. 1984, 57, 115. (21) Wilson, M. A. Applications of NMR in Soil Science and Geochemistry; Pergamon Press: Oxford, 1988. (22) Rullkotter, J.; Michaelis, W. Org. Geochem. 1989, 16, 829. (23) Derenne, S.; Largeau, C.; Casadevall, E.; Damste, J. S. S.; Tegalaar, E. W.; De Leeuw, J. W. Org. Geochem. 1985, 16, 873. (24) Hutton, A. C. Organic petrology of oil shales. Ph.D. Thesis, University of Wollongong, Wollongong, New South Wales, Australia, 1982; p 519. (25) Hutton, A. C. Organic Petrography of Rundle-Stuart Lamosite-A Case Study. Proceedings of the First Australian Workshop on Oil Shales; CSIRO Division of Energy Chemistry: Lucas Heights, NSW, Australia, 1983; p 31. (26) Hutton, A. C. Am. Assoc. Pet. Geol. Bull. 1984, 68 (8), 1055. (27) Knutson, C. F.; Dana, G. F.; Hutton, A. C.; Macauley, G. Am. Assoc. Pet. Geol. Bull. 1984, 68 (10), 1684. (28) Hutton, A. C. Aust. Coal Geol. 1985, 5, 25. (29) Evans, E.; Batts, B.; Cant, N. Fuel 1987, 66, 326. (30) Wilson, M. A.; McCarthy, S. A.; Collin, P. J.; Lambert, D. E. Org. Geochem. 1986, 9, 245. (31) Wilson, M. A.; Lambert, D. E.; Collin, P. J. Fuel 1985, 64, 1647. (32) Lambert, D. E.; Wilson, M. A. Prepr. Pap.sAm. Chem. Soc., Div. of Fuel Chem. 1985, 30, 256. (33) Saxby, J. D.; Lambert, D. E.; Riley, K. W. Fuel 1987, 66, 365.
Energy & Fuels, Vol. 12, No. 2, 1998 263 Table 1. Mineral Composition for Stuart and Condor Oil Shales concentration, % w/w component
Stuart
kerogen smectite illite kaolinite quartz feldspar pyrite siderite calcite ankerite dolomite gypsum anatase
22 27 5 6 16 5 2 3 7 2 3 2 0.2
Condor 16 16 24 35 1 6 2 0.7
amounts in these oil shales. It is moderately abundant in Stuart-Rundle but is sparse in Condor, which contains smaller lamalginite forms. Reptilian macrofossils have also been found in oil shales from the deposits, but only Stuart-Rundle contains abundant ostracod and mollusc shell fragments. These oil shales also differ in organic origin from other highly aliphatic Australian oil shales such as Tasmanite, which arises from a deposit of the unicellular algae Tasmanites punctatus.34,35 Elemental analyses showed that the Stuart kerogen contained 71.51% C, 9.99% H, 1.12% N, and 2.21% H2O. The Condor kerogen contained 65.63% C, 8.13% H, 2.20% N, and 2.56% H2O. Furthermore, both Stuart and Condor kerogens were found to contain ash (6.20% and 12.78%, respectively) after removal of organic matter by thermal treatment. The higher ash content of the Condor kerogen was due to a higher anatase content compared to the Stuart kerogen, as well as a trace amount of quartz in the concentrate as revealed in the X-ray spectra below. Kerogen was isolated from oil shale using two different procedures. These procedures rely on hydrofluoric acid (HF) to break any silicaceous bonds, thereby forming fluoride salts. These salts are then destroyed along with other minerals by the addition of other Bronsted or Lewis acids. The method of Robl and Davis,36 which was modified to suit our work, uses an in situ solution of boron trifluoride, generated from the reaction of boric acid and HF, to dissolve the fluoride salts. It is important to ensure that there is an excess of boric acid throughout the process so that no HF remains after the isolation process. This method is also appealing, since the generated BF3 reacts with HF to form soluble HBF4, thus keeping all species in solution. Polyethylene bottles were used in our initial studies, but because of the unusual findings of polymethylene in our kerogens, procedures were checked by using Teflon bottles. Both vessels were not responsible for the polymethylene in our isolated kerogens. Our modified procedure can be summarized as follows. A mass of oil shale containing about 6 g of kerogen was divided in half and placed into two 1-L bottles. A quantity of 600 mL of 12% HF was slowly added to each bottle, and after the initial reaction had subsided the bottles were capped and placed onto stirring plates. Any gas pressure buildup in the bottles was released about every hour for the first 3 h. The samples in the bottles were stirred overnight. The ensuing reaction is exothermic, so the bottles were placed in a bowl of crushed ice and water and allowed to equilibrate to prevent boiling and loss of BF3 and to protect the bottles from the heat change. Boric acid (85 g) was then slowly added to each bottle, and the bottles were shaken to facilitate mixing. The bottles were capped and the contents stirred overnight. (34) Regtop, R. A.; Crisp, P. T.; Ellis, J. Fuel 1982, 61, 185. (35) Boreham, C. J.; Wilkins, A. L. Org. Geochem. 1995, 23, 461. (36) Robl, T. L.; Davis, B. H. Org. Geochem. 1993, 20, 249.
264 Energy & Fuels, Vol. 12, No. 2, 1998 The suspension was filtered under reduced vacuum through a Buchner funnel. The kerogen was suspended in warm water (60 °C) to dissolve any unreacted boric acid and refiltered. The washing procedure was repeated four times. The isolated kerogen was air-dried and lightly crushed with a mortar and pestle. The second method used to isolate kerogen has been described previously.37-43 It uses HCl to destroy carbonate minerals and then HF/HCl to destroy and dissolve siliconbased minerals. Both techniques should destroy the mineral and clay components of the oil shale, with the exception of pyrite and anatase. Pyrite is not decomposed by hydrochloric or hydrofluoric acids and is believed to have a strong affinity for kerogen. Although pyrite is decomposed by oxidizing agents such as nitric acid or hydrogen peroxide, these reagents also attack the kerogen and were not used. Anatase (TiO2) was present in the original oil shale. It is inert to the reagents used in the isolation procedures and so remains in the kerogen. The resulting product of both these methods should be kerogen with some pyrite and anatase. The presence of pyrite and anatase in the kerogen does not interfere with NMR measurements. Other kerogen isolation experiments were performed on the Stuart oil shale using 1 N acetate buffer solution (82 g of sodium acetate plus 27 mL of glacial acetic acid) or 12% hydrochloric acid to destroy carbonate minerals and leave silica-based minerals in the sample. All spectra were obtained on a Bruker DRX 300-MHz instrument using cross-polarization (CP) or Bloch decay methods.21 The kerogens and oil shales were packed into 5-mm zirconia rotors with Kel-F caps and spun at speeds of 7 kHz. The CP experiments required up to 32 000 transients with a contact time of 1 ms and recycle delay of 2 s. Bloch decay spectra were collected with a 10-s recycle delay and 8-ms acquisition time. An 8 µs pulse was used, and the number of transients was 8000. The decoupler was turned on only during acquisition. Dipolar-dephasing experiments were performed with a 45-µs dephasing time using a conventional pulse sequence with a 180° refocusing pulse.21,44 The inversion recovery sequence with cross-polarization21 was used to measure carbon spin-lattice relaxation times. Blanks were run of rotors to ensure no artifacts in the spectra. The data were collected in 1 K of memory, zero-filled to 4 K, and then Fourier transformed using line-broadening factors of 20-50 Hz. All spectra were referenced to TMS (0 ppm). The low-field peak of adamantane was employed as a secondary reference (38.3 ppm). X-ray diffraction spectra for the isolated kerogens were generated on a Siemans Kristalloflex X-ray generator equipped with two powder cameras with Bragg-Brentano geometry. A Philips PW2276/20 X-ray tube was used at a power of 30 mA and 45 kV to produce cobalt X-rays. Samples of kerogen or oil shale were mounted in an aluminum sample holder, with dimensions of 44 mm long (in the plane of the X-rays), 12.5 mm wide, and 1.7 mm deep, holding a packed sample of about 0.40 g. The holder and sample were placed on the diffractometer and an XRD pattern collected from 3.00 to 90.00°, 2θ, at intervals of 0.04°, 2θ. Count times varied, but usually 10 (37) Durand, B., Ed. Kerogen: insoluble organic matter from sedimentary rocks; Technip: Paris, 1980; Chapter 2. (38) Eglington, G.; Murphy, M. T. J. Organic Geochemistry; Springer-Verlag: New York, 1969. (39) Newton, E. T. Geol. Mag. 1875, 12, 337. (40) Dancy, T. E.; Giedroye, V. J. Inst. Pet. 1950, 36, 593. (41) Kinney, C. R.; Schwartz, D. Ind. Eng. Chem. 1957, 49, 1125. (42) Down, A. L. J. Inst. Pet. 1939, 25, 230, 816. (43) Narbutt, J. Angew. Chem. 1922, 35, 238. (44) Wilson, M. A.; Pugmire, R. J.; Karas, J.; Alemany, L. B.; Woolfenden, W. R.; Grant, D. M.; Given, P. H. Anal. Chem. 1984, 56, 933.
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Figure 1. Solid-state 13C CP-MAS NMR spectra of (a) Condor oil shale and (b) isolated Condor kerogen. s/interval was employed to give a total count time of about 6 h for the 2176 data points/scan.
Results and Discussion 13C CP-MAS spectra and cross-polarization dynamics of oil shales have been extensively studied in the early 1980s using low fields (2.11 T or thereabouts) so that sidebands are absent from spectra at low spinning speeds (3.5 kHz or thereabouts). A number of studies have also been completed on shales from the geographical region from which samples in this study are drawn.21,30-33 It is sufficient to say here that for quantitation, lower fields are appropriate. In this work we have used fields of 7.05 T to assist in resolution of structural groups in the aliphatic region of the spectra (see below). The 13C CP-MAS NMR spectra of Condor oil shale and its kerogen extract are shown in Figure 1. The highly aliphatic nature of this oil shale is characterized by the intense peak at 32 ppm (line width at half-height, W1/2 ) 1152 Hz). No resolution of other aliphatic resonances is observed in the spectrum of the kerogen extract, although the resonance has a 32 ppm reduced W1/2 of 351 Hz. This result parallels that found for other kerogens45-49 in the literature. For example a kerogen sample of aromaticity similar to that of Stuart is shown in Zujovic et al.46 and appears identical. We also confirmed this for a Tasmanite kerogen sample. The Stuart oil shale samples, like Condor, are also similar to those aliphatic oil shales reported in the literature. In the case of Stuart oil shale, aromaticity fa ) 0.09 at 1 ms contact time (Figure 2), three regions of resonance are present in the aromatic region and there is a small but significant contribution from the carboxyl group, resonances in the region 173-185 ppm. Signals from phenolic carbons (including alkoxy aryl
(45) Miknis, F. P.; Jiao, Z. S.; MacGowan, D. B.; Surdam, R. C. Org. Geochem. 1993, 20, 339. (46) Zujovic, Z.; Srejic, R.; Vucelic, D.; Vitorovic, D.; Jovancicevic, B. Fuel 1995, 74, 1903. (47) Barakat, A. O. Energy Fuels 1993, 7, 988. (48) Boucher, R. J.; Standen, G.; Patience, R. L.; Eglington, G. Org. Geochem. 1990, 16, 951. (49) Bharati, S.; Patience, R. L.; Larter, S. R.; Standen, G.; Poppet, I. J. F. Org. Geochem. 1995, 23, 1043.
Polymethylene in Oil Shales
Figure 2. 13C CP-MAS NMR spectra of Stuart oil shale. Insert is the expanded region showing the carboxylic (173-181 ppm), phenolic (152 ppm), and other aromatic (125 and 130 ppm) resonances.
Figure 3. Aliphatic region of 13C-NMR spectra of Stuart oilshale kerogens: (a) CP-MAS spectrum of kerogen isolated using HCl/HF; (b) CP-MAS spectrum of kerogen isolated using HF/BF3; (c) Bloch decay spectrum of kerogen isolated using HF/BF3.
ether) are shown in the inset of Figure 2 at 149-155 ppm. Nevertheless, the majority of the signal belongs to aliphatic polymethylene carbons located at 32.4 ppm. Like Condor, the resonance is rather broad with a peak height at half-width (W1/2) of 256 Hz. The most significant feature of the aliphatic resonance of the Stuart kerogen 13C-NMR spectrum is the resolution of two carbon types at 32.6 and 30.3 ppm (Figure 3). This was the case for kerogens prepared by HF/HCl and HF/BF3 extraction (compare spectra a and b of Figure 3). These results also indicate a fundamental difference in the structure and bonding in the oil shale of Stuart compared with those of the oil shale of Condor. The resonances come from polymethylene resolved in slightly different chemical environments and, on chemical-shift grounds, cannot be assigned to methyl groups, which normally resonate upfield.21 Bloch decay (10-s recycle time) and CP-MAS (1-ms contact time) spectra show the resolved features, with the upfield resonance being more prominent in the Bloch decay spectrum (Figure 3c) probably because of its shorter spin-lattice relaxation time or better cross-
Energy & Fuels, Vol. 12, No. 2, 1998 265
Figure 4. Dipolar-dephased (45 µs) 13C MAS NMR spectrum of Stuart kerogens isolated using (a) HF/BF3, (b) HCl, and (c) sodium acetate.
polarization kinetics. Unlike the oil-shale spectrum, after dipolar dephasing44 for 45 µs the upfield resonance remains in the kerogen spectrum (Figure 4a). Dipolar dephasing is conventionally used to identify the degree of protonation of various carbons, owing to the C-H dipolar interaction being proton-substitution-dependent. We have shown that rapid molecular motion in polymethylene groups can also lead to weak dipolar interactions and hence long dephasing apparent spin-spin lattice relaxation times.50 It appears that the 30.3 ppm resonance is retained after dipolar dephasing because it is mobile polymethylene. This is consistent with a shorter spin-lattice relaxation time in the Bloch decay experiment. Moreover, inversion-recovery experiments show that the carbon spin-lattice relaxation time of the mobile polymethylene resonance differs from that of the other aliphatic resonances (CP T1(C) of 237 and 408 ms, respectively). It can be concluded that the removal of carbonate- and silicate-type minerals causes increased mobility of polymethylene. This may occur because the organic component is bound to the inorganic components or during the extraction process cross-linking units are hydrolyzed. The dipolar-dephased NMR spectrum of Stuart oil shale treated with only sodium acetate is shown in Figure 4c. Little of the polymethylene is preserved in the spectrum compared with that of the original oil shale. The dipolar-dephased spectrum of the Stuart oil shale treated with HCl shows a polymethylene resonance, though to a much lower degree (Figure 4b) compared with the kerogen isolated with HF/BF3. Both these acid treatments only remove carbonate minerals and do not affect silicaceous minerals and hence molecular motion of polymethylene is not increased by the extraction of the carbonate minerals alone. Checks were also made on kerogen samples from Rundle oil shales. As already noted, this deposit is contiguous with the Stuart deposit. NMR spectra and the behavior of the samples were identical with that of the Stuart samples. The isolated Stuart and Condor kerogens were analyzed by XRD and their spectra compared in Figure 5. (50) Wilson, M. A.; Batts, B. D.; Hatcher, P. G. Energy Fuels 1988, 2, 688.
266 Energy & Fuels, Vol. 12, No. 2, 1998
Figure 5. Comparison of X-ray diffraction patterns for (a) Stuart and (b) Condor kerogen isolated with HF/BF3. A ) anatase. P ) pyrite.
Lee et al.
phous material from the spectra. These organic humps have been well-documented in the literature for oil shales as well as coal.51-54 However, the sharpness of the peak, at about 24°, 2θ, on the top of the first large hump in the Stuart kerogen was unexpected. The Condor kerogen did not show this feature in its spectrum. It was first thought that this peak may have been due to a mineral salt formed during the isolation procedure. Ralstonite (∼Na(Mg1,Al5)6F12(OH)6‚3H2O) and fluorite (CaF2) are such salts that have been formed in previous studies.36,37 However, characteristic peaks for these salts are not present in the XRD spectra. A contaminant in the kerogen is also unlikely because all the kerogens were treated identically and this peak is present in the same kerogen isolated via different methods. Therefore, the peak at about 24°, 2θ is due to order in the kerogen structure confirmed as longchain free polymethylene groups by 13C solid-state NMR. It seems the mineral matter in the StuartRundle kerogen holds the polymethylene in a very random and amorphous way but that order is achieved after removing the mineral matter. It should be noted that the Condor kerogen did not show a sharp peak at 24°, 2θ, and the presence of free polymethylene groups was not detected in the NMR analyses. The Stuart-Rundle deposit clearly contains kerogen material that is less cross-linked than kerogens isolated from deposits of similar aromaticity, i.e., Condor. In the 13C solid-state NMR spectra of the oil shales this difference is not evident because the polymethylene chains are disordered because of entanglement with mineral matter, which causes larger chemical anisotropy and increased disorder. However, removal of mineral matter releases these chains so that they can be resolved in both NMR and X-ray diffraction spectra. The mineralogy of Stuart-Rundle and Condor is similar (Table 1). This discounts the unlikely supposition that different mineral-matter bonding reactions may alter the chemistry of the kerogen isolation procedure resulting in release of polymethylene in one case but not the other. It is concluded that the biological precursors are different because of different concentrations of Pediastrum species in the origin organic matter that gave rise to the oil shale. Pediastrum is common in StuartRundle but rare in Condor. Conclusion
Figure 6. Comparison of X-ray diffraction patterns for Stuart kerogens isolated using (a) HF/HCl (b) and HF/BF3. A ) anatase. P ) pyrite.
Typically, the spectra contain sharp peaks arising from both pyrite and anatase. Spectra for Stuart kerogen isolated by the two different methods are compared in Figure 6, and again, both show the presence of pyrite and anatase. As well as the sharp peaks observed due to the mineral inclusions, two broad humps are also observed in the spectra of Stuart and Condor kerogens. There is a larger hump centered about 24°, 2θ and another flatter hump centered about 46°, 2θ. These humps arise from the kerogen structure, which is shown to be an amor-
The kerogens in Stuart-Rundle and Condor oil shales, Queensland, Australia, are similar in that they are both highly aliphatic. However, the kerogen in StuartRundle is much less cross-linked. Hence, after removal of mineral matter, the polymethylene groups released show discrete ordering compared with the aliphatic carbon types in Condor kerogen. Resonances are seen at or about 30 ppm in 13C-NMR spectra, which have unusual dipolar-dephasing behavior. Polymethylene is also seen as a sharp peak in X-ray diffractograms in (51) Van Krevelen, D. W. Coal, 3rd ed.; Elsevier: Amstredam, 1993. (52) Hutton, A. C.; Mandile, A. J. J. Afr. Earth Sci. (Middle East) 1996, 23 (1), 61. (53) Mandile, A. J.; Hutton, A. C. Int. J. Coal Geol. 1995, 28 (1), 51. (54) Khorasani, G. K. Proceedings of the Second Australian Workshop on Oil Shale, St. Lucia, Australia, December 6, 7, 1984; CSIRO Division of Energy Chemistry: Lucas Heights, NSW, Australia; p 62.
Polymethylene in Oil Shales
Stuart-Rundle kerogen but not in Condor kerogen. It is proposed that the differences between the two oil shales are due to differences in the concentration of Pediastrum species present. Acknowledgment. We thank the UTS industry link Research fund and ARC postgraduate award industry
Energy & Fuels, Vol. 12, No. 2, 1998 267
for support. Mr. Chris Matulis and Ms. Anne Tibbett from CSIRO Division of Coal and Energy Technology are thanked for XRD and elemental analysis, respectively. Southern Pacific Petroleum NL is thanked for providing samples. EF970087I
