Petrographic and Chemical Properties of Carboniferous Resinite from the Herrin No. 6 Coal Seam

Resinite is a naturally occurring substance found in coal and derived from original plant resins. It is ubiquitous in North American coals and comprises 1 to 4% by volume of most Illinois coals. It has been commercially exploited in the western USA for use in adhesives, varnishes and thermal-setting inks. The major objectives of this study were: (1) to separate resinite macerals from the Herrin No. 6 coal seam and to carefully verify, by petrographic and fluorescence microspectrophotometric methods, that the separated material was indeed resinite; (2) to characterize the chemical composition of the separated resinite by Py–GC–MS techniques; and (3) to confirm the earlier results that show that this Carboniferous resinite was a much different chemical substance than the Cretaceous and younger resinites. An additional objective was to compare the separated resinite to the resinite being commercially exploited in the western USA. High purity fractions of resinite concentrates were separated from the Herrin No. 6 coal by a combination of density gradient separation and sink–float techniques. The chemical structure of the resinite concentrate indicated by the Py–GC–MS analysis is that of a straight chain aliphatic polymer much like common polyethylene. This result confirms the earlier work of Nip et al. [Nip, M. de Leeuw, J.W., Crelling, J.C., 1992. Chemical structure of bituminous coal and its constituent maceral fractions as revealed by flash pyrolysis, Energy Fuels 6, 125–136.]. The assumption that the resinites in the Illinois basin were similar in nature to the commercial resinites of the younger coals of the western USA appears invalid in the case of the resinite in the Herrin No. 6 coal. Although the botanical function of the Carboniferous resinite is at present unclear, it is clear that the cutinite and resinite precursors had not yet evolved to the point where they had differentiated into significantly different chemical compounds

Organic Geochemical and Petrographic Analysis of Pure Macerals from the Ohio Shale

Recent advances now permit the separation of coal into constituent macerals of high purity using density gradient centrifugation (DGC). With the availability of pure macerals, the chemical structure of each can be investigated separately, without the interactive interference of the other macerals or mineral matter. The present study is a preliminary effort applying these methods to the study of oil shale kerogen. We have used a sample from the Huron Member of the Upper Devonian Ohio Shale from Logan County, Ohio. Whole rock petrographic examination revealed intact Tasmanites, telalginite of unknown derivation and a weakly fluorescing matrix. Pyrite is abundant, including framboidal and euhedral pyrite imbedded within macerals. The kerogen concentrate was subjected to DGC. The resulting profile shows a single, broad main peak, consisting of mixed telaginite, amorphinite and rare vitrinite. Variable amounts of entrapped minerals apparently account for the broad range of density within the peak, with the organic assemblage being fairly consistent. In future work, it is recommended that the kerogen be micronized prior to DOC to permit a cleaner separation. In order to investigate the chemistry of macerals, pyrolysis is preferred over simple extraction, since soluble native bitumen is mobile and may migrate from the maceral of origin into a neighboring one, acting as a natural contaminant. Pyrolysis techniques assure that the data reflect the nature of indigenous material only. The Ohio Shale kerogen and 4 DGC fractions were subjected to micro-scale, anhydrous, in vitro pyrolysis, followed by GCMS of the saturate and aromatic LC fractions of the pyrolyzate. The 4 DGC fractions are nearly identical in both their saturate and aromatic molecular distributions, consistent with the petrographic observations. To further demonstrate the efficacy of the method, a pure sporinite isolated from a coal in the Pennsylvanian Brazil Formation of Indiana was also analyzed. The sporinite pyrolyzate can readily be distinguished from that of the Ohio Shale alginite by the distributions of n-alkanes, isoprenoids, phyllocladane derivatives, extended tricyclic terpanes, hopanes, moretanes, steranes, alkylbenzenes and thiophene derivatives. Py-LC-GCMS is an effective and versatile characterization tool, as it provides a great number of molecular parameters

Geochemical Characterization of Maceral Concentrates from Herrin No. 6 Coal (Illinois Basin) and Lower Toarcian Shale Kerogen (Paris Basin)

Density gradient centrifugation (DGC) is a physical method for the separation of sedimentary organic matter into its constituents. Using DGC, it is possible to prepare maceral concentrates from a single sample, which are amenable to microanalysis. DGC fractions from a coal sample from the Illinois Basin (Herrin No. 6, Upper Carboniferous) and from the kerogen of a marine shale sample from the Paris Basin (Lower Toarcian) were analyzed by flash pyrolysis-gas chromatography-mass spectrometry, after extraction by CH2Cl2. Chemical differences between the coal DGC fractions are the easiest to recognize, indicating very distinctive biological precursors. For example, the liptinite fraction ( = 1.12 g ml-1) is dominated by long-chain aliphatic compounds (n-alkanes and n-alkenes) along with alkylbenzenes and alkylphenols. Vitrinite (1.29 g ml-1) shows a predominance of alkylbenzenes and phenolic compounds. Polyaromatic hydrocarbons (especially naphthalene, phenanthrene, anthracene and their pseudohomologues) are major compounds in the pyrolyzate of fusinite (1.45 g ml-1). In contrast, there is less variety of organic compounds in the Toarcian sample. Petrographically, this kerogen is primarily amorphous. However, a main DGC peak ( = 1.18 g ml-1) with two shoulders (1.15 and 1.23 g ml-1) is resolved using multi-step centrifugation. The chemical differences between these fractions are subtle but significant. Concentrations of alkylbenzenes, alkylthiophenes, alkylpyrroles and phenolic compounds increase with density, relative to the aliphatics. This indicates that this kerogen, probably of algal and bacterial origin, is partially separable by DGC

Classification of Torbanite and Cannel Coal. I. Insights from Petrographic Analysis of Density Fractions.

Torbanite and cannel coal are considered to be coals because of their low mineral content and overall physical morphology. However, the texture and composition of the organic matter in torbanite and cannel coal are similar to the kerogen occurring in oil shales and lacustrine source rocks. Therefore, understanding the nature and origin of organic components in torbanite and cannel coal is of significance in the study of kerogen and petroleum formation. In this research, a set of torbanites and cannel coals from different locations throughout the world were petrographically characterized and processed using a density gradient centrifugation (DGC) technique. Microscopically, the torbanite and cannel coal are composed of coarser maceral particles set in a fine-grained to amorphous groundmass. The groundmass is a mixture of more than one type of substance and accounts for 10 to 80% (by volume) of the torbanites and cannel coals. Botryococcus-related alginite is the most characteristic component of the torbanite. While sporinite typically is the main phytoclast in the cannel coals, in most cases the groundmass is volumetrically the dominant component, determining the overall character of the sample. This observation calls into question the traditional practice of classifying such coals using the alginite to sporinite ratio. Variations in composition, texture and fluorescence permits the recognition of three different types of groundmass: lamalginitic, bituminitic and vitrinitic. High purity alginite, sporinite, vitrinite and varieties of groundmass were separated using the DGC technique. The distribution of density fractions closely reflects the petrographic composition of the various torbanites and cannel coals. Distinct peaks on the density profiles represent the major organic components and peak magnitudes are functions of the percentage of the components, demonstrating that the density gradient profiles can be used to distinguish the different types of torbanite and cannel coal. The separation data also indicate a gradual shift towards higher density from lamalginitic to bituminitic to vitrinitic groundmass

Characterization of Organic Sulfur Compounds in Coals and Coal Macerals

Peroxyacetic acid oxidation has been used to investigate the type and distribution of organic sulfur species in samples of vitrinite, sporinite and inertinite, separated from the Herrin No.6 and an Indiana No.5 coal seam. It was established that organic sulfur species were selectively preserved during oxidation and their analysis led to some of the first sulfur-33 NMR spectra obtained for coal. The effects of maceral separation processes on model compounds were also studied. Results from our studies support the following conclusions: 1). Different macerals have different distributions and types of organic sulfur species. 2). Organic sulfur compounds in coal occur at the ends of macromolecular structures. 3). Maceral separation techniques do not affect organic sulfur species in coal. 4). Maceral separation is essential for the chemical characterization of coal. 5). GC-MS and sulfur-33 NMR data agree

Aspects of Sporinite Chemistry

With the recent advent of the ability to separate coal into maceral concentrates of high purity, the individual constituents of coal can now be analyzed separately, without their mutual interference, giving a much better understanding of the macromolecular structure of coal. The sporinites from two Pennsylvanian age coal samples (Illinois Basin, U.S.A.) were studied, one from a vitrinite-rich high-volatile bituminous coal, the other from a liptinite-rich high-volatile bituminous coal of slightly higher rank. Sporinites were isolated from each coal by density gradient centrifugation. The sporinite of the vitrinite-rich coal was compared chemically and petrographically with the parent coal and with the sporinite of the liptinite-rich coal. The fluorescence spectrum of the sporinite from the liptinite-rich coal is shifted to the red end of the spectrum, which may be accounted for by the somewhat higher rank of the sample and/or by differences in the original assemblage of spores. The lack of chemical differences between the extracts of the sporinite and its whole coal reinforce the concept of bitumen as an homogeneous mobile phase pervading the coal. Thus, extract chemistry seems an unsuitable technique for distinguishing between macerals from the same coal. Hopane and sterane distributions in the sporinite and parent coal pyrolyzates are very similar, but the two materials can be readily distinguished by the distribution of tetracyclic diterpanes of the phyllocladane type, which are biological marker compounds derived from higher plant material. Overall, the sporinite is considerably more paraffinic in character and has a greater preponderance of straight-chain alkane moieties than the coal as a whole. In the case of the vitrinite-rich coal, the whole-coal structure appears significantly more polyaromatic than the sporinite. The distributions of thiophenic compounds differ in the pyrolyzates of the two materials. The sporinite from the liptinite-rich coal is even less polycondensed than the sporinite from the vitrinite-rich sample. The chemical and petrographic differences of the two sporinites probably reflect the different assemblages of spores in the original peats and their different diagenetic histories

Organic Geochemistry of a Lower Jurassic Synrift Lacustrine Sequence, Hartford Basin, Connecticut, U.S.A.

Synrift terrestrial strata of the Lower Jurassic East Berlin Formation (Hartford basin, Connecticut, U.S.A.) record cyclical expansion and contraction of major lakes, six of which were deep enough to develop anoxic bottom waters. We have studied one representative lacustrine sequence in detail, sampling a new roadcut near the village of East Berlin. The section examined is 4 m thick, with a gray siltstone at the base, deposited in shallow water, overlain by an organic-rich black shale (deep water), succeeded in turn by another gray siltstone, deposited as the lake waters gradually receded. The upper gray siltstone is chemically distinct from the lower siltstone, as it contains small amounts of corrensite, analcime and gypsum, reflecting the increasing salinity and alkalinity of the contracting lake. The samples in the center of the black shale unit contain laminae of thermally-altered, yellowish orange-fluorescing, mottled telalginite. The fluorescence properties indicate a peak oil generation maturity level, confirmed by a vitrinite reflectance of 1.13% and a Methylphenanthrene Index of 1.08. The other samples have less organic matter, becoming increasingly lean towards the top and bottom of the sequence. Samples in the middle of the black shale unit are distinguished by the presence of an homologous series of tricyclic terpanes extending from C20 to at least C41 , and by the near absence of hopanes and steranes. Moving upsection into the gray siltstone, the samples contain markedly less extractable organic material (EOM) and the concentration of tricyclic terpanes relative to hopanes steadily decreases. In the uppermost sample, hopanes are the predominant terpanes. Moving downsection from the black shale into the lower gray siltstone, EOM and the ratio of tricyclic terpanes also decrease, except in the lowermost samples, which contain terpane distributions like those of the middle part of the black shale. This likely is migrated material, because bitumen fills microfractures and extensive megafractures. The lack of hopanes and steranes in the black shales cannot simply be a maturation effect, as these biomarkers appear in the adjacent beds. Instead, the unusual terpane distributions may indicate a changing depositional environment, documenting the geochemical evolution of the lake. Or, more likely, they may result from fractionation during expulsion of petroleum from these mature source rocks

The nature and fate of natural resins in the geosphere. XII. Investigation of C-ring aromatic diterpenoids in Raritan amber by pyrolysis-GC-matrix isolation FTIR-MS

Upper Cretaceous amber from the Raritan Formation (Sayerville, New Jersey) has been investigated by Pyrolysis-GC-MS and Pyrolysis-GC-matrix isolation FTIR-MS. Results establish the existence of two distinct forms of amber in this deposit. Both forms are Class Ib ambers, but they are unambiguously differentiated on the basis of their (intact) diterpenoid composition. The presence of callitrisate in both forms, and cupraene in samples designated form 1, strongly suggest that both derive from related-but-distinct species within the Cupressaceae. In addition to callitrisate, dehydroabietate and analogous 17-nor-, 16,17-dinor- and 15,16,17-trinor- analogues of these compounds are also observed. The distributions of these products in multiple samples suggest that they are the result of biological emplacement, rather than diagenetic modification of the parent compounds. This indicates that the distributions of diterpenes observed in these samples are representative of the original bioterpenoids and, hence, are useful for chemotaxonomic analyses

Characterization and Selective Removal of Organic Sulfur from Illinois Basin Coals

In order to develop appropriate desulfurization strategies, the organic sulfur species and their distribution in coal need to be characterized. Peroxyacetic acid oxidation has been developed to render coal soluble, allowing for the subsequent GC-FID/FPD and GC-MS analysis of sulfur compounds. Four Illinois Basin coals and samples of sporinite, vitrinite and semifusinite isolated from them have been examined. Between 20 and 50% of the organic sulfur in these coals is associated with relatively few compounds detected in the volatile oxidation products. Of these, methylsulfonic acid is the most abundant, which, from model compound studies, results from oxidation of either methyl disulfide or simple thiophene structures in the coals. Although the species detected are commonly occurring among the majority of the coal and maceral fractions, their distribution varies considerably from sample to sample. By fractionating the oxidation products, a fraction was obtained that had a sulfur content of 18%. This fraction represents nearly 50% of the total organic sulfur but only 10% of the weight of the coal. Using peroxyacetic acid to desulfurize coal, it has been demonstrated that all pyrite and sulfate can be removed at room temperature and at least 25% of the organic sulfur at slightly higher temperatures

Organic Geochemical Characterization of the Density Fractions of a Permian Torbanite

Two distinct organic components, the Botryococcus-related alginite (Reinschia) and the amorphous organic matrix, were isolated by high-resolution density gradient centrifugation (DGC) from a Permian torbanite (New South Wales, Australia). On the density profile, the alginite (1.03-1.10 g/ml) and the matrix (1.16-1.21 g/ml) appear to be two distinct peaks. With fluorescence microscopy, the alginite shows bright yellow to orange fluorescence and well-preserved algal structure, whereas the matrix has a reddish brown fluorescence of medium intensity. The H/C and O/C atomic ratios indicate that the alginite is equivalent to a Type I kerogen, whereas the matrix falls into the Type II kerogen category. The more heavy O and S, and less light H content in the matrix also helps in explaining the higher density of the matrix relative to the alginite. Flash pyrolysis-GC/MS of the CH2Cl2-extracted density fractions shows that the pyrolyzates of both the alginite and the matrix are dominated by normal alk-1-enes and alkanes, which range up to C31. However, these normal hydrocarbons are relatively more abundant in the alginite than in the matrix. The alginite also produced a n-α-ω-alkadiene series which was not detected in the matrix. Compared to the alginite, the matrix pyrolyzate is enriched in C19C31 straight-chain aliphatics and aromatic, phenolic and hopanoid compounds, suggesting that the matrix was formed through incorporation of degraded algal material and humic matter. The higher Methylphenanthrene Index (MPI) value of the matrix pyrolyzates relative to the alginite indicates that the MPI is affected by organic matter type