F.X.C. de las Heras

Characterization of Tertiary Catalan lacustrine oil shales: Discovery of extremely organic sulphur-rich Type I kerogens

Abstract The kerogens of three Tertiary Catalan lacustrine oil shales were analyzed by light microscopy, flash pyrolysis-gas chromatography-mass spectrometry, and bulk composition methods (elemental analysis, Rock Eval pyrolysis). Two of the three kerogens (Ribesalbes and Campins) are extremely rich in organic sulphur (atomic Sorg/C ratio > 0.04) and hydrogen (atomic ratio H C ratio > 1.5) and are, consequently, classified as Type I-S kerogens. Very characteristic distribution patterns of flash pyrolysis products (e.g., alkan-9- and -10-ones, alkadienes) of the Ribesalbes kerogen revealed that it is predominantly composed of fossilized organic matter of the freshwater alga Botryococcus braunii. These two findings demonstrate that sulphurization of organic matter may also occur in lacustrine sediments provided that sulphate is supplied by external sources. Data on the third kerogen sample (Cerdanya) suggest that the freshwater alga Pediastrum may contain a (partly) aromatic biomacromolecule that is selectively preserved upon diagenesis. These findings testify to the large variability in palaeodepositional conditions in lacustrine environments. A comparison of the biomarker composition of the extract of the Ribesalbes oil shale with the kerogen composition indicate that biomarkers often cannot be used to assess the major sources of organic matter in such settings. A similar conclusion can be drawn from a comparison of literature data concerning the Messel Oil Shale.

Molecular analysis of sulphur-rich brown coals by flash pyrolysis-gas chromatography-mass spectrometry: The type III-S kerogen

The molecular composition of five brown coals from three different basins (Maestrazgo, Mequinenza and Rubielos) in Spain was investigated by flash pyrolysis-gas chromatography and flash pyrolysis-gas chromatography-mass spectrometry. In these techniques, the macromolecular material is thermally degraded in an inert atmosphere and the compounds formed are on-line separated, identified and quantified. This information provided insight into the macromolecular structure of the coals which was inaccesible by other means. The composition of the pyrolysates is described in detail with emphasis on the distributions and relative abundance of n-alkanes, n-1-alkanes, (alkyl)phenols, sulphur compounds [(alkyl)thiophenes and (alkyl)benzenes and (alkyl)naphthalenes. These compound classes represent the major pyrolysis products of the samples analysed and were used to assess the contributions of specific biomacromolecules mainly originating from higher plants. One of the five brown coal samples investigated is so rich in organic sulphur (one sulphur atom for every 9-15 carbon atoms as determined by elemental analysis) that a new kerogen type (Type III-S) describing the kerogen contained in this coal is defined. Type III-S kerogen is defined as a kerogen with high atomic S org./C (0.04) and O/C (0.20) ratios. Two of the five brown coals samples investigated contain a series of long-chain alkylbenzenes with an unprecedented carbon number distribution pattern with a second maximum at C18. This unusual distrubution pattern is thought to originate from the presence of long-chain alkylbenzene moieties bound via a heteroatom(presumably an ether bond) to the macromolecular coal matrix preferentially at position 12 in the alkyl side-chain of these moieties.

A study of sulfur functionalities in fossil fuels using destructive- (ASTM and Py-GC/MS) and non-destructive- (SEM-EDX, XANES and XPS) techniques

Abstract A set of Spanish coals and oil shales were studied using destructive and non-destructive techniques to identify the functionalities of the sulfur compounds. The selected samples included organic-sulfur-rich Spanish lignites mined in the Mequinenza, Utrillas and Calaf basins; calcareous source-rocks from Organya and sulfur-rich oil shales from Ribesalbes. Using analytical pyrolysis coupled to gas chromatography–mass spectrometry, we estimated the ratio Sorg/C in these coals and oil shales, and compared them with those obtained by the ASTM method D2492. Also, a scanning electron microscope (SEM) coupled to an energy-dispersive X-ray spectrometer (EDX) allowed the direct determination of organic sulfur content in coals. Two major non-destructive techniques, XANES and XPS, were used to investigate sulfur functionalities, such as pyritic, sulfidic, thiophenic, sulfoxide, sulfone, sulfonate and sulfate forms. The study shows that sulfur characterization in coal is not without difficulties and no method is exempt from problems and the introduction of possible artifacts.

Characterization of humic acid from leonardite coal: an integrated study of PY-GC-MS, XPS and XANES techniques

Abstract We studied the humic-acid fraction isolated from a Spanish leonardite coal (Torrelapaja, Cretaceous basin belonging to the Utrillas facies) using a suite of chromatographic and spectroscopic techniques to characterize the structure of the carbon skeleton and the nature of the sulfur-containing compounds. In particular, analytical pyrolysis coupled to gas chromatography-mass spectrometry was used to gain detailed molecular information on the organic structures. Pyrolysis in the presence of a methylating agent (tetramethyl-ammonium hydroxide, TMAH) was used to characterize polar moieties. We employed non-destructive techniques, XANES and XPS, to investigate the composition of the sulfur functionalities (such as sulfide, polysulfide, thiophene, sulfoxide, sulfonate and sulfate). The combination of these different approaches allows a more complete understanding of the organic sulfur structures in the leonardite coal. In agreement with previous studies, our results show that oxidized sulfur functionalities, such as sulfonate and sulfate, represent the major forms of sulfur in leonardite coal.

Sulphur-binding in recent environments. I. Lipid by-products from Ni2B desulphurization

Selected geochemically relevant model compounds were subjected to the nickel boride desulphurization method. Poor hydrogenating properties of this agent were observed in the case of sterically hindered double bonds. Apart from its desulphurizing properties, a significant number of functionalities present in lipid compounds were transformed on treatment with nickel boride. Ketones were reduced to their alcohols whereas aldehydes were partly converted to their ketals. Although alcohols and esters were unaffected by this agent, a nearby unsaturation (i.e., position α) resulted in the loss of the alcohol group and cleavage of the ester bond, respectively. The significance of these results was demonstrated by desulphurization experiments on polar fractions from two recent sediment extracts. The main compound among the apolar products obtained, phytane, was found to be quantitatively derived from phytol and not, as may be presumed, from its macromolecularly sulphur-bound precursor. The results of this work show that compounds generated by nickel boride desulphurization of polar fractions from lipid extracts, particularly from recent sediments, are not necessarily derived from their sulphur-bound precursors. Conclusions with regard to the palaeoenvironmental significance of the hydrocarbons formed, therefore, should be made with caution.

Novel C-ring cleaved triterpenoid-derived aromatic hydrocarbons in Tertiary brown coals

Abstract Five novel ethylene-linked polymethyl-substituted phenyl/naphthyl or naphthyl/naphthyl hydrocarbons have been identified in aromatic hydrocarbon fractions of immature Tertiary coals using liquid chromatography, gas chromatography (GC), and GC coupled to mass spectrometry. These compounds are produced during coalification through triterpenoid aromatization processes that involve C-ring opening (C8(14) bond cleavage) and preservation or loss of the A-ring. This second type of reaction is illustrated here for the first time. Structures corresponding to various degrees of aromatization have been found, indicating that these hydrocarbons undergo further aromatization after C-ring cleavage. All these compounds are observed to occur only in coals corresponding to diagenetic conditions that have also resulted in the formation of C-ring preserved triterpenoid-derived hydrocarbons containing more than two aromatic rings.

Characterization of Azo Dye (Acid Red 14) Removal with Granular Activated Carbon: Equilibrium and Kinetic Data

Abstract The work describes the sorption of an azo dye (Acid red 14) from aqueous solution onto Granular activated carbon (GAC) in order to characterize the sorption properties. Batch experiments were performed to determine loading isotherms at different pH values and evaluate the effect of the surface functional groups of the sorbent and the dye acid‐base properties. The loading equilibrium data were modelled with Langmuir, Freundlich, and Redlich‐Peterson isotherms. The maximum dye sorption capacity of GAC was determined as 31 g kg−1 at neutral and basic pH values. Kinetic experiments were carried out at different pH values and Acid Red 14 (AR14) concentrations. Three theoretical models (Pseudo first, pseudo‐second order reaction models, and the Elovich model) were used to describe the dye sorption kinetics. The sorption rate constants were determined by graphical analysis of the proposed models. The study showed that sorption followed a pseudo‐first order reaction model although the pseudo‐ second order reaction model provides an acceptable description of the sorption process.