Chemical Structural Investigation of Asphaltenes and Kerogens by Pyrolysis-Methylation

Chemical structural investigation of asphaltenes and kerogens by pyrolysis-methylation

J. C. DEL Rio, F. MARTiN, F. J. GONZALEZ-VILA and T. VERDEJO Instituto de Recursos Naturales y Agrobiologia de Sevilla, C.S.I.C., P.O. Box 1052, 41080 Seville, Spain

(Received 22 December 1994; returned for revision I I July 1995; accepted 21 December 1995)

Abstract-Molecular characterization of kerogen and asphaltene fractions isolated from three oil shales taken from the Puertollano deposit has been carried out by pyrolysis-methylation. Long-chain n-alkanes, n-alk-I-enes, long-chain carboxylic acid methyl esters and aromatic compounds were the major thermal degradation products obtained for both kerogen and asphaltene fractions. Different monomeric and dimeric lignin-derived compounds were also released. The use of pyrolysis-methylation provides additional information about the chemical structural composition of the macromolecular organic matter comprising kerogens and asphaltenes at a molecular level, to that gained from conventional pyrolysis. The chemical structures of the released products indicate that considerable amounts of functionalized compounds are bound to the macromolecular structure of asphaltenes and kerogens via ester and ether linkages. Copyright IQ 1996 Elsevier Science Ltd

Key words-asphaltenes, kerogen pyrolysis, pyrolysis-methylation of kerogen, fatty acids in kerogen pyrolysates, polar compounds

INTRODUCTION 1993a). The results of Py-GC-MS have improved our knowledge considerably of the chemical macromol- The molecular characterization of asphaltene and ecular structure of kerogens and asphaltenes. kerogen fractions, isolated from different fossil fuels, However, one should realize that only a part of the has been the subject of numerous investigations organic matter can be analyzed and that some (BChar and Pelet, 1985; Mycke and Michaelis, 1986; moieties can be drastically altered due to the nature Goth er al., 1988; Barakat and Yen, 1990; Stout, of the technique. Pyrolysis seems to underestimate the 1991; Strausz et al., 1992; Barakat, 1993). Asphalt- presence of carboxyl-bearing units among the enes are generally considered to be composed of small structural building blocks. In fact, flash pyrolysis of solubilized, less-condensed kerogen moieties (Tissot polymers containing benzenecarboxylic acid moieties and Welte, 1984). Knowledge of the chemical nature (such as fulvic and humic acids) leads to biased of these geopolymers may help to provide a better structural interpretations since it has been shown that understanding of the source of precursor materials, these units undergo decarboxylation in this process the environmental conditions of deposition, and the (Martin et al., 1994). Consequently, our view of the type of diagenetic, catagenic and maturation pro- molecular composition of kerogens and asphaltenes cesses involved. The great complexity of both may be very limited, and possibly highly biased, when fractions has hindered the formulation of individual based on conventional pyrolysis data. molecular structures, although a number of different Recently, pyrolysis in the presence of tetramethyl- models have been proposed for kerogen (Oberlin ammonium hydroxide (TMAH) has been introduced et al., 1980; Bthar and Vandenbroucke, 1987). for the detection of benzenecarboxylic acids by A wide variety of methods has been applied to the pyrolytic methods (Martin et al., 1994; Saiz-Jimenez, study of asphaltenes and kerogens. Bulk methods, 1994). This technique, also called “simultaneous such as elemental analysis, FT-IR and solid-state pyrolysis methylation”, produces methyl esters of NMR spectroscopy give useful overall information, carboxylic acids and methyl ethers of phenols; while chemical and thermal degradative techniques aliphatic hydroxy compounds become partially provide more detailed molecular information. Since methylated (Challinor, 1989). It has been demon- the early 198Os, pyrolysis-gas chromatography-mass strated that the reaction that takes place involves spectrometry (Py-GC-MS) has been widely used in thermally assisted chemolysis rather than the the structural investigation of asphaltenes and methylation of released pyrolysis products (de Leeuw kerogen (van de Meent et al., 1980; Larter and and Baas, 1993; Martin et al., 1994). This technique Douglas, 1982; Bthar and Pelet, 1985; Tannenbaum has already been successfully applied in structural et al., 1986; Hartgers et al., 1992; de1 Rio et al., elucidation studies of different natural and artificial 1010 J. C. Del Rio et cl/. polymers such as cutins, natural resinites, alkyd prepared as suspensions in TMAH. The syrups were resins, polyester fibres, lignins and humic substances placed on the ribbon foil of the CDS pyroprobe and (Challinor. 1989, 1991a, b; Anderson and Winans, heated to 500 C for 10 s. Separation of the pyrolysis 1991; de Leeuw and Baas, 1993; Saiz-Jimenez et al.. products was achieved on a 25 m x 0.2 mm id. fused 1993, 1994; Martin et al., 1994. 1995~ b; del Rio silica capillary column (SE-52; J and W Scientific). et al.. 3994b; Hatcher et a/., 1994; Hatcher and The gas chromatograph (Hewlett Packard HP-5890) Clifford, 1994; Chiavari rt al.. 1994). was programmed from 40 C to 300 C at a rate of In this paper, we present data for the analysis by 6 Cmin. Helium (1 ml/‘min flow rate) was used as pyrolysissmethylation of a set of kerogens and carrier gas. The mass spectrometer (HP 598X A) was asphaltenes isolated from oil shales. The aim is to set at 70 eV. Identifications were achieved by mass study the feasibility of using pyrolysissmethylation fragmentography, library search and comparison for the structural characterization of kerogen and with literature data. When possible. identifications asphaltenes. The study will provide information on were accomplished by comparison with authentic the polar moieties bonded to the macromolecular standards. The substitution patterns of the different structure of asphaltenes and kerogens through ester positional isomers were established by comparison of linkages. Kralert et al. (1991) and Challinor (1991 b) relative retention times with literature data and. when have already presented some preliminary data for the possible. confirmed by co-injection with authentic use of pyrolysis-methylation in the characterization standards. of aliphatic ester moieties in kerogens and coals. Nuclear magnetic resonance High resolution solid-state “C-NMR spectra of the MATERIALS AND METHODS kerogen and asphaltene samples were collected at 25.2 MHz under cross polarizationmagic angle The oil shale samples were taken from the spinning conditions (CP/MAS) using the quanti- Puertollano (Ciudad Real, Spain) deposit. The tation conditions described elsewhere (Friind and geological setting of this oil shale. from the Liidemann, 1991). Stephanian B, has already been described (Wallis, 1983; Wagner, 1985). The organic geochemical characterization of the bituminous fractions has also RESULTS AND DISCUSSION been published (de1 Rio er ul., 1993b. 1994a). Two samples were collected from the Emma mine, at two Figure I shows the ‘C-NMR spectra of the different strata of increasing depth (Emma I and kerogen and asphaltene samples isolated from the Emma 2). The other sample was taken from the B selected oil shales. The quantitation of the different seam at the Calve Sotelo mine (PB). spectral regions is shown in Table 2. The spectra Raw oil shale samples were milled and extracted show two broad signals in the “aliphatic” (5546 ppm) exhaustively with methylene chloride:methanol (2: 1). and “aromatic” (I lo-160 ppm) regions and indicate Minerals were removed by successive treatments with a structural similarity between the kerogen and 20% HCI (12 h, 6OC) and HCl:HF (1: 1) (24 h, 6O“C, asphaltene samples. A higher aliphaticity was twice). The kerogens were thoroughly rinsed with observed in the kerogens than in their associated water until the washings were free of chloride ions asphaltenes. The band in the aliphatic region may and then dried. Aliquots of the oil shale extracts were reflect the contribution to the organic matter of these dissolved in a minimum amount of chloroform and materials of highly aliphatic, non-hydrolyzable the asphaltenes precipitated by adding a 30-fold biopolymers similar to those recently described in excess of n-pentane. Asphaltenes were separated by different organisms (Largeau et al., 1984, 1986; Nip centrifugation, and subsequently recovered by decan- et al., 1986; Kadouri et al., 1988; de Leeuw et al., tation. The precipitation process was repeated twice 1991). In fact, the alga Botryococcus braunii, whose in order to purify the asphaltenes. presence has been described in the Puertollano oil The pine and beech milled wood lignins (MWL) shales (Gomez-Borrego, 1992), possesses a highly used in this study were prepared from extracted pine (Pinus pinea) and beech (Fagus silcatica) by ball milling and extracting with dioxanelwater as de- Table I. Elemental analysts and atomic ratios of the kerogen and scribed by Bjiirkman (1956). asphaltene samples (on a dry, ash-free basis)

The elemental analysis and atomic ratios of the PB Emma I Emma 2 kerogen and asphaltene fractions are shown in KUQgWl KWJgll Ker0getl asphaltene Table I. asphaltene asphaltene C 78.0 74.0 76.0 68.3 79 0 74.2 H 10.4 8.7 X.8 1.7 8.4 7.3 Pyrolysis-gus chromatography-muss spectrometr? N 1.6 3.0 1.7 3.9 2.2 3.1 (0 + S,‘,,)’ 10.0 143 13.5 20. I 10.2 15.4 The samples (l-2 mg) were first moistened with H/C 1.60 I.41 1.39 1.35 I .28 I.18 IO-20 ~1 of TMAH (25% aqueous solution) and o:c 0.10 0.14 0. I3 0.22 0.10 0.15 dried in a desiccator overnight. Kerogens were * by difference. Chemical structural investigation of asphaltenes and kerogens 101 I

Kerogen PB

160 b PPm PPm Fig. 1. Solid-state ‘V-NMR of the asphaltene and kerogen fractions isolated from the selected oil shale samples. The integration values for the different spectral regions are given in Table 2.

aliphatic biopolymer called algaenan, which shows a moieties, were also released after pyrolysis-methyl- “C-NMR spectrum dominated by a broad band with ation. a sharp maximum at 29 ppm, corresponding to polymethylenic chains (Largeau et al., 1984; Kadouri Hydrocarbons et al., 1988). Aliphatic compounds were identified in the Unfortunately, the NMR data obtained cannot pyrograms as series of n-alkanes and n-alkenes, with provide further information at the molecular level. chain lengths up to C,,. Distributions of alkane/ Pyrolytic techniques have been shown to be excellent alkene pairs were similar to those obtained after complementary techniques for providing additional conventional pyrolysis (de1 Rio et al., 1993a) and insights at the molecular level. Because of the known indicate the presence of significant amounts of limitations of conventional pyrolysis (Martin et al., polyalkyl components in the structures of the 1994; Saiz-Jimenez, 1994) in elucidating the chemical kerogens and asphaltenes, in accordance with structure of macromolecular organic matter, we have ‘%-NMR observations. As previously suggested for used pyrolysis-methylation or pyrolysis in the similar materials, the major contributors to the alkyl presence of tetramethylammonium hydroxide, which components might be non-saponifiable, highly provides additional information. aliphatic biopolymers such as those recently Figure 2 shows the chromatograms (FID) of the identified in present-day and fossil plant cuticles and thermal degradation products released after pyroly- in the cell walls of some algae species (Nip et al., sis-methylation of the kerogens and asphaltenes 1986; Largeau et al., 1984, 1986; Kadouri ef al., respectively. The main compounds identified were 1988). As stated above, one of these biopolymers, series of alkanes/alkenes, long-chain carboxylic acid referred to as algaenan, occurs in the outer cell walls methyl esters and benzenecarboxylic acid methyl of the common green algae Botryococcus braunii. esters. Some triterpenoid compounds with hopanoid Remains of B. braunii have recently been reported in skeletons, as well as compounds arising from lignin these oil shales (Gbmez-Borrego, 1992). Such biopolymers yield, on conventional pyrolysis, a series of n-alkane+alkenes with a distribution similar to that found in our pyrolyzates (Largeau et al., 1986). Table 2. Integration values (% area) for the different regions of the ‘C-NMR spectra of the kerogen and asphaltene samples Although these biopolymers are minor constituents of the original biomass, they are more refractory than PB Emma I Emma 2 Kerogen Kerogen Kerogen other major organic components and may be asphaltene asphaltene asphaltene subsequently enriched in the sediment during 110-160 ppm 22 33 20 39 25 42 diagenesis (Tegelaar et al., 1989; de Leeuw er al., 5-46 ppm 78 67 80 61 75 58 1991). 1012 J. C. Del Rio et al.

Long-chain carboxylic acids methyl esters samples after pyrolysis-methylation. In general, the A series of long-chain carboxylic acid methyl esters distributions of fatty acids show a slight even-over- from C8 up to Cj6 was also produced, indicating that odd predominance and maxima at C,, and C8. these moieties are present in the structure of the Kralert et a/. (1991) also observed the release of kerogen and asphaltene. The m/z 74 mass chro- long-chain carboxylic acid methyl esters with an matograms presented in Fig. 3 shows distributions of even-to-odd predominance after pyrolysis-methyl- the series of long-chain carboxyhc acids (as methyl ation of kerogens. Likewise, Barakat (1993) obtained esters) released from the kerogen and asphaltene different series of fatty acids with an even carbon

Kerogen Pb

c25 (

Kerogen EMMA I

c25, , / / c30

I Kerogen EMMA 2

20 30 Retention time (min)

Fig. 2. (a) Chemical structural investigation of asphaltenes and kerogens 1013

Asphaltenes PB

Asphaltenes EMMA 1

Asphaltenes EMMA 2

IO 20 30 40 50 Retention time (min)

Fig. 2. (b) Fig. 2. (a) FID chromatograms of the products released after pyrolysis-methylation of the kerogen samples. (@-(COOMe)>: benzenedicarboxylic acid dimethyl ester, C, indicates the n-alkane/+alkene chain length). (b) FID chromatograms of the products released after pyrolysis-methylation of the asphaltene samples. (@-(COOMe)*: benzenedicarboxylic acid dimethyl ester, C. indicates the n-alkaneln-alkene chain length). number predominance from Monterey kerogen by boxylic acid dimethyl esters were also identified in all alkaline hydrolysis. of the samples: they had a strong even-over-odd Series of 2-methoxy fatty acid methyl esters, predominance. At this point it is not known whether w-methoxy fatty acid methyl esters and cl,w-dicar- the methoxyl groups are originally present as such or 1014 J. C. Del Rio et al. derive from the TMAH. In the latter case, the and G compounds, could not be detected in the hydroxyl groups could be present either in the free samples. A striking feature, however, was the release form, or linked to the macromolecular network via of unsaturated Ck8, and C,.+, fatty acid methyl esters ether bonds. All of these series were more after pyrolysis-methylation, present in comparatively predominant in the asphaltenes than in the respective low concentrations. These unsaturated moieties may kerogens. Minor amounts of 2-methyl fatty acid have been incorporated and preserved within the methyl esters ranging from C26 to Ci4 with a kerogen and asphaltene macromolecular network, maximum at CXOwere detected only in the kerogens and not previously detected, possibly due to the fact from Emma I and Emma 2. Fatty acids characteristic that the methods used have been very drastic or not of a bacterial input, such as the iso- and anteiso-CIS appropriate. Unsaturated fatty acids have been

Kerogen PB

Kerogen EMMA 1

lLLi?lcl6 18

Kerogen EMMA 2

c25

I I I

Retention time (min)

Fig. 3. (a) Chemical structural investigation of asphaltenes and kerogens 1015 released from these kerogens by room temperature aliphatic moieties than the n-alkanesln-alkenes. This alkaline permanganate oxidation (de1 Rio et al., is supported by the fact that there is no parallel 1993~) and also from Monterey kerogen by alkaline between the chain-length distribution of n-carboxylic hydrolysis (Barakat, 1993). acids and their equivalent hydrocarbons in the The fact that the series of n-alkanesln-alkenes, and asphaltene or kerogen pyrolyzates. long-chain carboxylic acid methyl esters, are released The above series may be collectively derived from upon pyrolysis-methylation seems to suggest that the ester-bound long-chain carboxylic acids protected in long-chain carboxylic acids arise from different the most refractory part of the macromolecular

cl6

1 (-18 Asphaltenes PB

I Asphaltenes EMMA 1

Asphaltenes GO EMMA 2

Retention time (min)

Fig. 3. (b)

Fig. 3. (a) m/z 74 Mass chromatograms showing the distribution of fatty acids (as methyl esters) released from the kerogen samples. (b) m/z 74 Mass chromatograms showing the distribution of Fatty acids (as methyl esters) released from the asphaltene samples. J. C. Del Rio et al.

1-L m I L 1”.~,““1’~“1‘~“I”“I”“,~‘.‘,““,““, IO 25 20’ Retention time (min)

Fig. 4. Partial summed mass chromatogram of the ions m/z 163, 221, 279 (for the benzenedi-, tri- and tetracarboxylic acid methyl esters, respectively), m/z 165, 196 (for the dimethoxybenzenecarboxylic acid methyl esters) and m/z 211, 226 (for the trimethoxybenzenecarboxylic acid methyl esters), showing the distributions of benzenecarboxylic acid moieties in a representative sample.

network. Kawamura and Ishiwatari (1985) defined asphaltenes also release larger amounts of methylated the tightly bound carboxylic acids as those only hydroxyacids, particularly for the PB sample. released on pyrolysis. Tightly bound carboxylic acids are generally considered to originate from the Aromatic compounds incorporation of partly altered lipids, directly The main aromatic compounds released after inherited from living organisms, into kerogens at an pyrolysis-methylation were the benzenecarboxylic early stage of sedimentation (Harrison, 1978; Peters acids (as methyl esters) and their methoxylated et al., 1981; Taylor et al., 1984; Kawamura and counterparts. The major compounds were the Ishiwatari, 1985; Kawamura et al., 1986; Largeau benzenedicarboxylic acid methyl esters in all samples. et al., 1986; Jaffe and Gardinali, 199 1; Derenne et al., Benzenetri- and benzenetetracarboxylic acids (as 1991). However, for torbanites, tightly bound methyl esters) were also released, although in lesser carboxylic acids were shown to be directly inherited amounts. Different methoxylated benzenecarboxylic from the source organism, the colonial microalga acid moieties, such as 3,4-dimethoxybenzenecar- Botryococcus braunii (Largeau et al., 1986). In fact, boxylic acid and 3,4,Qrimethoxybenzenecarboxylic pyrolysis-methylation of the biopolymer afgaenan acid were other important aromatic components released fatty acid methyl esters from Cl4 to Cl8 as the released from these samples. Figure 4 shows a partial dominant products (McKinney et al., 1995). summed mass chromatogram of the distribution of The long-chain carboxylic acids released on benzenecarboxylic acids and their methoxylated pyrolysis were linked to the macromolecular network counterparts obtained for kerogen PB, which is via sterically protected, and hence, non-hydrolyzable, typical of those obtained for the kerogens and ester bonds. Subsequently, such acids would be asphaltenes investigated. The presence of carboxylic protected from diagenetic degradation and would be acids and their methoxylated counterparts is of released only during laboratory heating experiments interest as they represent the final steps in the or during natural catagenic evolution (Kawamura oxidation of the side chains in the lignin macromol- et al., 1986; Jaffe and Gardinali, 1991). ecule. These benzenecarboxylic acids represent The apparent similarity of the distributions of structural constituents of the asphaltene and kerogen bound carboxylic acids in the asphaltene and macromolecules, not previously identified by conven- respective kerogens indicates a close compositional tional pyrolytic techniques, and are probably present relationship between the two geopolymers. However, in the macromolecular matrix either free or linked by some minor differences can also be observed between ester bonds. the kerogens and the respective asphaltenes. The fatty Dimeric thermal degradation products of lignins acids released from the asphaltenes show a predomi- were also generated on pyrolysis-methylation. The nance of the higher homologues and a stronger mass spectrum and the structure of a lignin dimeric even-over-odd predominance in this region with compound is shown in Fig. 5. It was identified as a respect to their corresponding kerogens. The syringoresinol-type (A) by comparison with a mass Chemical structural investigation of asphaltenes and kerogens 1017

spectrum available in a commercial library (Wiley) pure lignins. Figure 6 shows a comparison of the m/z and is shown in Fig. 5. It was identified in all the 18 I mass chromatograms of the thermal degradation asphaltene samples and in minor amounts in the products obtained after pyrolysis-methylation of kerogen of Emma 2. The identity of this compound asphaltenes PB and beech lignin. It can be seen that was also confirmed by comparison with the compound A is present in both pyrolyzates, compounds released after pyrolysis-methylation of suggesting that it is a characteristic lignin pyrolysis

446 A 0CH3

169

50 loo 150 200 250 300 350 400 450 500 mlr 4

207

L 522 200 250 300 350 400 450 m/z I C

Fig. 5. Mass spectra of some compounds identified as lignin dimers. A: pinoresinol-structure. B and C: unknowns. 1018 J. C. Del Rio et al.

Asphaltenes lignin

Beech lignin m/z 181

(b)

30 35 40 45 Retention time (min) Fig. 6. Comparison of the m/z 18I mass chromatograms of the compounds released from (a) Asphaltenes PB and (b) beech lignin. Peak labels correspond to the compounds referred to in Fig. 5.

product. The mass spectra of two other related dation products. On the other hand, the presence of compounds (B and C) observed in the m/z 18 1 mass lignin-derived moieties has already been shown in the chromatogram of Fig. 6, and not yet identified, are Messel oil shale kerogen using mild hydrogenation also shown in Fig. 5. Several other dimeric compounds (Mycke and Michaelis, 1986). were also detected in the kerogen and asphaltene pyrolyzates by comparison with the products released Hopanoid compounds after pyrolysis-methylation of different lignins. This is Pyrolysis-methylation also released hopanoid the case for a cluster of compounds observed in the compounds from the asphaltenes and kerogens. m/z 410 mass chromatogram of beech and pine lignin Hopanoid compounds have previously been released and also released from the asphaltenes and kerogen from other kerogens and asphaltenes by conventional samples. Figure 7 shows a comparison of the m/z 410 pyrolysis and chemical degradation methods (Tan- mass chromatogram of the compounds released after nenbaum et al., 1986; Barakat and Yen, 1990; pyrolysis-methylation of asphaltenes PB and beech Barakat, 1993). The main compounds released from lignin and a representative mass spectrum of one of our samples were hopanoic acid methyl esters, these compounds. In general, all of these aromatic hopanes and hopenes. A representative m/z 191 mass components detected in the kerogen and asphaltene chromatogram showing the distribution of hopanoid pyrolyzates might derive from higher plant lignins and compounds is presented in Fig. 8. The identities of possibly also from tannins and would therefore be the different compounds, assessed by mass fragmen- indicators of a terrestrial origin. Since the original tography and relative retention times published in the lignin from which these compounds are derived is not literature, are listed in Table 3. The distribution of the soluble, the occurrence of lignin-derived materials in hopanoid compounds released was similar in all of the asphaltene fractions seems to suggest that these the samples, with 17a(H),2lb(H) and 17/I(H),2la(H) compounds represent low molecular weight degra- hopanes and hopanoic acid methyl esters being Chemical structural investigation of asphaltenes and kerogens 1019

Asphaltenes PB I m/z 410

Beech lignin m/z 410

(b)

) .Jl*, .-. . . . - 40 Retention time (min) Fig. 7. Comparison of the m/z 410 mass chromatograms of the compounds released from (a) Asphaltenes PB and (b) beech lignin. A representative mass spectrum, corresponding to the marked chromatographic peak, is shown in the upper corner. predominant. All identified triterpenoids belong to CONCLUSIONS the hopane family, and no triterpenoids characteristic of terrestrial higher plants, such as oleananes The structural characterization of the kerogen and and ursanes, were found. The abundance of hopanes asphaltene fractions isolated from the Puertollano oil indicates a contribution from bacteria to the oil shale shale has been approached by the use of pyrolysis in organic matter. The fact that hopanoic acids are the presence of tetramethylammonium hydroxide released from the kerogen matrix by pyrolysis-meth- (TMAH), the so-called pyrolysis-methylation. In ylation indicates that they are bonded at their side contrast to conventional pyrolysis, pyrolysis-methyl- chain to the complex network of the kerogen and ation releases considerable amounts of functionalized asphaltene, presumably through an ester linkage. compounds bound to the macromolecular structure Hopanoid compounds bound through ether bonds of kerogens and asphaltenes. The main compounds are released as hopenes since the aliphatic alcohols released were series of alkanes/alkenes, long-chain do not become methylated. The identification of carboxylic acid methyl esters, methylated benzenecar- hopenes substantiates previous suggestions that boxylic acids, lignin-derived aromatic units and significant amounts of triterpanols are linked via hopanoid compounds (hydrocarbons and carboxylic ether bonds to the geopolymeric matrix. However, acids), indicating that polar compounds are also part the possibility that hopenes may derive from of the macromolecular structure of these materials. hopanoid carboxylic acids via decarboxylation due The release of polar compounds from the macromol- to inefficiencies in the methylation procedure, should ecular networks of geopolymeric materials has not be ruled out. usually been approached by tedious, time-consuming I020 J. C. Del Rio et al

Hopanoid hydrocarbons

Hopanoic acids

Retention time (min) Fig. 8. m/z 191 Mass chromatogram showing the hopanoid distribution in a representative sample. The assignments of the different chromatographic peaks are listed in Table 3.

methods, such as chemical degradations. The use of Associate Editor-P. Hatcher pyrolysis-methylation is a fast, sensitive, one-step procedure for the analysis of geomacromolecules Ackno~l,led~emmts~We wish to thank the Comisibn containing polar functionalities, and requires very Interministerial de Ciencia y Tecnologia (CICyT) for providing financial support (project PB91-0074). and minor amounts of sample. Finally. the results further Professor H.-D. Liidemann for recording NMR data. support previous suggestions of a broad similarity between the structure of asphaltenes and kerogens derived from a given source rock, although REFERENCES some minor differences could be appreciated be- Anderson K. and Winans R. (1991) Nature and fate of tween them. natural resins in the geosphere. I. Evaluation of pyrolysis-gas chromatography/mass spectrometry for the analysis of natural resins and resinites. Ann/. Chwn. 63, Table 3. Hopanoid compounds ldentlfied in the pyrolyzates 2901-2908. Barakat A.D. and Yen T.F. (1990) Distribution of Hopanoid Iy~drocurhom pentacyclic triterpenoids in Green River otl shale kerogen. I trisnorhopene C27:I Org. Geochem. 15, 299-31 I. 2 22.29.30-trisnorhop-17,21-ene Barakat A.D. (1993) Carboxylic acids obtained by alkaline 3 17x(H)-22.29.30~trisnorhopane hydrolysis of Monterey kerogen. Energy and Fuels 7, 4 17B(H)-22.29.30-trisnorhopane 988-993. 5 norhopene C29: I BChar F. and Pelet R. (1985) Pyrolysis-gas chromatography 6 17s(H).Zl~(H)-30.norhopane 7 norhopene C29: I applied to organic geochemistry. Structural similarity 8 17/I(H).2ln(H)-30-norhopane between kerogens and asphaltenes from related extracts 9 hopene C30: I and oils. J. Anrd. Appl. P~wl. 8, 173-187. IO 17x(H),ZI~(H)-hopane Behar F. and Vandenbroucke M. (1987) Chemical II hopene C30: I modelling of kerogens. Org. Geochem. 11, I S-24. I2 I7p(H).Zla(H)-hopane Bjijrkman A. (1956) Studies on finely divided wood. Part I. I3 homohopene C3 I : I Extraction of lignin with neutral solvents. Seen. Hqxmi~ a&\ Papperstidn. 5913, 471485. I4 17?(H).2l/J(H)-hopanolc acid ME (22s) Challinor J.M. (1989) A pyrolysis-derivatisatlongas chro- I5 17~(H),218(H)-hopanoic acid ME (22R) matography-mass spectrometry technique for the struc- 16 17/J(H),ZIz(H)-moretanoic actd ME (22s) tural elucidation of some synthetic polymers. J. Anal. I7 17/3(H).Zla(H)-moretanoic acid ME (22R) Appl. Pyrol. 16, 323-333. I8 17x(H).ZI/j(H)-homohopanoic acid ME (22s) I9 I7a(H).ZI[$(H)-homohopanoic acid ME (22R) Challinor J.M. (1991) Structure determination of alkyd 20 I7[QH).Zln(H)-homomoretanoic acid ME (22s) resins by simultaneous pyrolysis methylation. J. Anal. 21 17i(l(H),ZIx(H)-homomoretanoic acid ME (22R) Appl. Pwol. 18, 233-244. 22 17z(H),2l[I(H)-bishomohopanoic acid ME (22s) Challinor J.M. (1991) The scope of pyrolysis methylation 23 17x(H).2lfl(H)-bishomohopanoic acid ME (22R) reactions. J. Awl. Appl. P~wl. 20, 15-24. 24 17/j(H).2lx(H)-bishomomoretanoic acid ME (22R) Chiavari G.. Torsi G., Fabbri D. and Galletti G.C. (1994) ME: methyl ester. Comparative study of humic substances in soil using Chemical structural investigation n of asphaltenes and kerogens 1021

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