Energy & Fuels 1988,2, 105-108 NH3 decomposition reaction. . We developed a kinetic model to account for NH3 generation from organic and inorganic N sources and for NH3 decomposition. We plan to generalize and refine the model as more data on NH, evolution and decomposition become available.
105
Acknowledgment. Ken Foster's contribution to our experimenta and Dr. Hugh Gregg's help with the computer for TQMS data manipulation are gratefully acknowledged. Registry No. NH3, 7664-41-7.
Novel Identification of 17@(H)-Hopanoidsin Green River Oil Shale Kerogen? Assem 0. Barakat* Department of Chemistry, Alexandria University, Alexandria, Egypt
Teh Fu Yen* Environmental and Civil Engineering, University of Southern California, Los Angeles, California 90089-0231 Received June 10, 1987. Revised Manuscript Received August 24, 1987 Green River oil shale kerogen was prepared by HCl/HF treatment and extensive Soxhlet extraction (C6H6/CH30Ha t azeotropic ratio) before and after mineral removal. The kerogen was subjected to mild stepwise oxidation using Na2Cr207in glacial CH3COOH. The oxidation products as their methyl esters were analyzed by capillary gas chromatography and combined gas chromatography-mans spectrometry. A dominant series of 17p(H)-hopane derivatives (Cm-C& were identified. The presence of these compounds suggests a significant algal contribution during diagenesis and points toward a mild thermal history for this Green River oil shale sample. Introduction Most chemical studies on oil shale have been directed toward the elucidation of biological markers (compounds thought to be directly related to common biological precursor material).'s2 The emphasis on the search for triterpenoidal alkanes is a reflection of current interest in this field. It is now firmly established that triterpenoids of the hopane family (C27-C35) are valuable biological markers for organic matter from bacterial or terrestrial sources.3-6 Moreover, certain stereochemical changes that take place in these molecules are useful as indicators of the degree of m a t u r a t i ~ n . ~ ~ ~ However, due to the complexity of the kerogen structure, previous investigations have dealt mainly with pyrolysis products and solvent-soluble extracts.,&10 Kerogen constitutes the bulk of organic matter in sediments and represents a potential source of contamination-free biomarkers.l' A deeper understanding of both the biological and diagenetic processes that contribute to the genesis of the shale organic matter necessitate the characterization of these compounds in kerogen. Recently, we have carried out exhaustive oxidative degradation of Green River oil shale kerogen using Na2Cr20,/glacial CH3COOH under mild conditions.12 This reagent is known to attack the CH group of alkanes a t a rate determined by the hydrocarbon structure; the approximate relative oxidation rates being 1:114:7000-18000 for methyl, methylene, and methine groups, respecti~ely.'~J~Also, it has been verified experimentaily16that polycyclic olefins (usually steroids and terpenes) are converted to a,p-unsaturated compounds in good yields. Evidence is reported here from capillary gas 'Presented at the Symposium on Advances in Oil Shale Chemistry, 193rd National Meeting of the American Chemical Society, Denver, CO, April 5-10, 1987.
0887-062418812502-0105$01.50/0
G R E E N RIVER K E R O G E N
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Figure 1. Schematic outline of the experimental procedures.
chromatography-mass spectrometry (GC/MS) data for provisional identification of a series of 17P(H)-hopane (1) Vandenbroucke, M. In Kerogen, Insoluble Organic Mutter from Sedimentary Rocks; h a n d , B., Ed.;Editions Technips: Paris, 1980; pp 420-425. (2) Tissot, B.P.; Welte, D. H. Petroleum Formation and Occurence; Springer-Verlag: West Berlin, 1984; pp 93-130. (3) Brassel, S.C.; Eglinpton, G.In Aduances in Organic Geochemistry, 1981; Bjoroly, M., Ed.; Wiley: Chichester, U.K., 1983; pp 684-697. (4) Van Dorsselaer, A.;Ensminger, A.; Spyckerelle, C.; Dastillung, M.; Sieskind, 0.;Arpino, P.; Albrecht, P.; Ourisson, G. Tetrahedron Lett. 1974,14, 1349-1352. (5) Mattern, G.;Albrecht, P.; Ourisson, G.J. Chem. SOC.D . 1970, 1570-1571. (6) Seifert, W. K.;Moldowan, J. M. In Aduances in Organic Geochemistry, 1979; Douglas, A. C., Maxwell, J. R., E%.; Pergamon: Oxford, 1980; pp 229-237.
0 1988 American Chemical Society
Barakat and Yen
106 Energy & Fuels, Vol. 2, No. 1, 1988 in.(
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Figure 2. Reconstructed ion chromatogram of the methylated products obtained from the first stage of NazCr207/CH3COOHoxidation of Green River Formation oil shale kerogen. derivatives (C30-C33)in the extracts of the primary oxidation products. Experimental Section Kerogen was prepared by using a raw sample from Green River oil shale from the Anvil Point oil shale mine. The raw shale was crushed to pass a 140-mesh Tayler screen and exhaustively extracted in a Soxhlet apparatus with C6H,/CH30H at azeotropic ratio. Minerals were removed from the oil shale by sequential treatment with 20% HCl(l2 h, 20 "C), 20% HC1/48% HF (3 days, 20 "C),and 20% HCl (2 h, 20 "C). The acid-leached material was washed successively with hot distilled water until the filtrate was neutral, dried,and again exhaustively extracted with the same solvent. The kerogen concentrate thus obtained was free of solvent-soluble material and contained 4.3 % ash. A 4.0517-g sample of kerogen concentrate was oxidized in five steps by stirring with a solution of 3.2 g of Na2Cr207per step in 80 mL of glacial CH3COOHfor a period of 20 h. The filtrates of each step were worked up separately according to the scheme outlined in Figure 1. The temperature was kept at 20 "C during the first oxidation period and was raised to 40 "C during each subsequent 20-h period. The detailed procedure was described previously.lZ The degradation products were esterified with 14% BF3/MeOH, and analyzed by capillary gas chromatography (GC) and computerized gas chromatography-mass spectrometry (CGC-MS). Analytical GC analysis was carried out on a Hewlett-Packard &MOA by using a 30 m X 0.25 mm i.d. WCOT SE54 glass capillary column. GC/MS analyses were performed with a Model 9610 Finnigan GC adapted for capillary chromatographyand interfad (7)Ensminger, A.; Albrecht, P.; Ourisson, G.;Tissot, B. Aduances in Orzanic Geochemistry. 1975; Campos, R., Goni, J., Eds.; Enadisma: Midrid, 1977; pp 45-52. (8)VitoroviE, D.; Mirjana, S. ACS Symp. Ser. 1983,No. 230,37-58. (91 Rullkotter, J.: Aizenshtat, Z.: Sdro, B. Geochim. Cosmochim. Acta 1984;48,pp 151l157. (10) Seifert, W. K. Geochim. Cosmochim. Acta 1987,42,p p 473-484. (11)Gallegos, E. J. In Oil Shale; Yen, T. F., Chilingarian, G. V., Eds.; Elaevier: Amsterdam, 1976;pp 149-180. (12)Barakat, A. 0.; Yen, T. F. Fuel 1987,66,587-593. (13)Mares, F.;Rocek, J. Collect. Czech. Chem. Commun. 1961,26, 2370. (14)Cainelli, G.; Cardillo, G. Chromium Oxidations in Organic Chemistry; Springer-Verlag: West Berlin, 1984;pp 8-23. (15)Dauben, W. G.; Ashcraft, A. C. J. Am. Chem. SOC.1963,85,3673.
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Figure 3. Mass fragmentogram ( m / z 191) and total ion current (RIC) obtained by GC/MS analysis of the primary oxidation products. Abbreviations N and D represent saturated n-monocarboxylic and saturated a,w-dicarboxylicacids, respectively; numerals following indicate the number of carbons. AME = acid methyl ester. with a Fmigan 4OOO quadrupole ma88 spectrometer. The column used was a 30 m X 0.25 mm i.d. fused silica column (DB-5). The instrumentation technique and operating conditions have been described in greater detail elsewhere.lZ Mass spectral data acquisition was performed by an INCOS 2300 computer system.
Results Five steps were necessary for complete degradation of Green River kerogen. The tohd yield was 2.738 g (=71% of the original organic matter). The solid residue obtained in the final step (0.2120 g) contained 0.0378 g organic matter (0.97% relative to original organic matter). The reconstructed ion chromatogram of the esterified products obtained in the first oxidation stage is shown in Figure 2. The distributions of pentacyclic triterpanes are best studied in GC/MS by monitoring the m / z 191 ion, which is a major fragment in these terpane series. Figure
Energy & Fuels, Vol. 2, No. 1, 1988
Identification of 17/3(H)-Hopanoids 1-
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According to the mass spectral features in Figure 4, the following acids were identified in the form of their methyl esters: (J) 17P(H)-hopanoic acid (C31H5202); (K) 17P(H)-homohopanoic acid (C32HMO2); (L) l7P(H)-bishomohopanoic acid (C33H5602);(M) 17P(H)-trishomohopanoic acid (C34H5802). The identifications were based on the
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following observations: (1)The fragment ion with mjz 369 is present in the mass spectra of all four compounds suggesting the loss of a side chain from a hopanoid skeleton. (2) The intense ions a t mjz 235, 249, 263, and 277 are fragments representing the B side of the molecule; monitoring these ions (see Figure 5) along with the total ion current quickly revealed the presence of a homologous series. (3) The assignment of the stereochemical configuration was based on the relative intensities of the fragmentation ion A ( m / z 191) and that of the fragmentation ion B (mjz 235, 249, 263, and 277 for J, K, L, and M, respectively), since it has been shown16that in the trans 17P(H) isomers the ratio A/B is less than 1, while in the cis 17a(H) isomers the ratio is greater than 1. (4) The fragmentation patterns of compounds K and L (Figure 4) were found to be equivalent with those of published spectra for the methyl esters of 17P(H),2lP(H)-homohopanoic and 17@(H),2l@(H)-bishomohopanoic acids.8 Therefore, mass spectrometric fragmentation patterns suggest that these compounds are all members of the same series having the same basic skeleton and only differing one from another by the length of their side chain.
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(16) Ensminger, A.; van Dorsselaer, A.; Spyckerelle, C.; Albrecht, P.; Ourisson, G . In Aduances in Organic Geochemistry, 1973; Tissot, B., Bienner, F., Eds.; Edition Technips: Paris, 1974; pp 245-260.
Energy & Fuels 1988,2, 108-110
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Discussion Saturated alkanes with a hopane-type skeleton occur in significant concentration in the geosphere4J7and have been isolated from various types of sedimentary organic matter.18J9 In addition to the parent C30 hydrocarbon, compounds with degraded (Cw,C,) and extended side chains (CN-C3J are commonly detected.I7 Due to the insolubility and macromolecular nature of kerogen, previous investigations on oil shales have been concerned with both the kerogen pyrolysis products and the solvent-extractable organics from the shale. Results based on the former method, which must involve considerable pyrolytic rearrangements, are of lesser interest from the paleobiochem(17) Van Domelaer, A.; Albrecht, P.; Ourisson, G. Bull. SOC.Chim. Fr. 1977, 165. (18) Ourisson, G.; Albrecht, P.; Rohmer, M. Pure Appl. Chem. 1979, 51, 709-729. (19) Youtcheff, J. S.; Given, P. H.; Baset, Z.; Sundaram, M. S. Org. Geochem. 1983,5(3), 157-164.
ical viewpoint. The present investigation provides valuable proof that a series of l7P(H)-hopanes (c3O-c33)are chemically bonded to the complex network of Green River kerogen. Hopanoids are widely distributed among bacteria and cyanobacteria (blue-green algae) and are also known to be present in certain higher plants, such as ferns.5 While it is commonly accepted that hopanes with 30 or fewer carbon atoms are derived from a C30 hopanoid, hop-22(29)-ene, known to be a constituent of several living organisms,20the extended hopanes (C3o-C35) have recently been related to a C35 precursor, bacteriohopanetetrol, which has been isolated from various microorganisms.18p21v22 It is therefore tempting to suggest an important contribution of prokaryotic organisms during diagenesis of Green River shale. Several authors6p7have indicated that pentacyclic triterpanes of the hopane family undergo structural changes under the effect of thermal stress. This involves transformation during diagenesis of the less stable 17p(H),21/3(H)isomers, which occur in the living system, to the more stable 17a(H),21@(H)isomers, which do not occur in the living system. The prominence of the l7(3(H)-isomers thus points toward a mild thermal history for this Green River oil shale sample. Acknowledgment is made to the binational Fulbright Commission for the Research Grant received by A.O.B. Partial support was received from the donors of the Petroleum Research Fund, administered by the American Chemical Society. Registry No. J, 110611-20-6; J (methyl ester), 110528-88-6; K, 54311-29-4; K (methyl ester), 110528-89-7;L, 54311-30-7; L (methyl ester), 62125-72-8; M, 54422-58-1; M (methyl ester), 110528-90-0. (20) Arpino, P.; Albrecht, P.; Ourisson, G. In Advances in Organic Geochemistry, 1971; von Gaertner, H. R., Wehner, H., Eds.; Pergamon: Oxford, 1972; pp 173-187. (21) Rohmer. M.: Ourisson. G. Tetrahedron Lett. 1976.40.3633-3636. (22) Forster,'H. J.; Biemkn, K.; Haigh, W. G.; Tattrie, N: H.; Calvin, J. R. Biochem. J. 1973,135, 133-143.
Communications Improving the Reliability of Quantitative Solid-state l3C NMR Analysis of Coal?
Sir: Previous investigations have shown that a significant fraction of the carbon atoms in coals and coal macerals are invisible to solid-state 13CNMR analysis regardless of the pulse excitation sequence emp1oyed.l We recently have devised a simple chemical method that largely circumvents this problem. Several lines of evidence suggest that organic free radicals and paramagnetic minerals both contribute to the loss in 13CNMR signal strength; the organic radicals are particularly a problem. Recent work in our laboratories 'Work performed under the auspices of the Office of Basic Energy Sciences, Division of Chemical Sciences, US.Department of Energy, under Contract No. W-31-109-ENG-38.
supports this viewpoint. First, the observable carbon contents (% Cobsd) measured by reliable spin-counting techniques are inversely related to the free-radical concentrations measured in ESR experiments. To examine the signal loss phenomenon in more detail, a Utah resinite sample was doped with varying amounta of a stable organic radical: 1,3-bis(diphenylene)-2-phenylallyl radical (BDPA). This resinite was selected for its low free-radical concentration and high solubility in methylene chloride. Indeed previous spin-counting experiments1 showed that 100% of its carbon atoms could be observed. The high solubility of the maceral enabled the preparation of a uniform mixture of resinite and the free radical by simultaneous deposition of an intimate solid mixture of the materials (1) Botto, R. E.; Wilson, R.; Winans, R. E. Energy Fuels 1987,1, 173.
0887-0624/88/2502-OlO8$01.50/0 0 1988 American Chemical Society
