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Figure 50. Pyrolysis mass spectra of (a) a recent redwood and (b) a brown coal (Herzogenrath lignite). Note the obvious decrease of the cellulose and hemicellu-lose fragment series (m/z 43, 55, 57, 58, 60, 72, 74, 84, 85, 86, 96, 98, 102, 112, 114, 126, 128, 144) in the lignite spectrum with respect to the recent redwood (indicated by arrows). Conditions: samples 10 yg; Tc 510°C; Egl 14 eV.

The relative intensity of hydrocarbon series, e.g., alkenes, naphthalenes and benzenes, increases with rank. That the differences between the spectra in Figure 51 are indeed mainly due to rank was established by Meuzelaar et al. (ref. 194) in a study of over 100 coals from the Rocky Mountain Province. However, this study also showed that the influence of differences in depositional environment on the pyrolysis patterns is often difficult to distinguish from the influence of differences in rank. The effects of depositional environment and degree of coalification on conventional

Figure 51. Pyrolysis mass spectra of three coal samples of different rank from the Uintah Region in the Rocky Mountain Coal Province (USA). Note the rapid decrease in dihydroxybenzenes (m/z 110, 124, 138) followed by phenols (m/z 94, 108, 122, 136) and sulphur-containing ions (m/z 34, 48, 64) as opposed to the strong increase in naphthalenes (m/z 142, 156, 170, 184, 198), benzenes (m/z 92, 106, 120, 134) and alkenes (m/z 56, 70, 84). Each spectrum was obtained by averaging quadruplicate analyses. Conditions: samples 50 yg; Tc 610°C; EeT 15 eV.

Figure 51. Pyrolysis mass spectra of three coal samples of different rank from the Uintah Region in the Rocky Mountain Coal Province (USA). Note the rapid decrease in dihydroxybenzenes (m/z 110, 124, 138) followed by phenols (m/z 94, 108, 122, 136) and sulphur-containing ions (m/z 34, 48, 64) as opposed to the strong increase in naphthalenes (m/z 142, 156, 170, 184, 198), benzenes (m/z 92, 106, 120, 134) and alkenes (m/z 56, 70, 84). Each spectrum was obtained by averaging quadruplicate analyses. Conditions: samples 50 yg; Tc 610°C; EeT 15 eV.

coal parameters, e.g. elemental composition, moisture content, calorific value, etc., have been authoritatively described by Teichmuller and Teichmuller (ref. 195).

No spectra of coals of higher rank than medium volatile bituminous are shown here because the highly condensed aromatic nature of such coals results in abundant char formation accompanied by very low yields of detectable pyrolysis products (see also Chapter 5.1). However, it should be pointed out that the rank of a coal is to a large extent independent of it's age. Some low rank, e.g. high volatile bituminous, coals were deposited during the Carboniferous Period whereas the medium volatile bituminous coal shown in Figure 51 (c) is only of Cretaceous age but was coalified more rapidly because of locally high geothermal gradients.

Van Graas et al. (refs. 73, 196) analysed series of coal samples by Py-MS and Py-GC/MS. They demonstrated that the spectra can be explained in terms of the maceral ("coal mineral") composition of the samples. The pyrolysis mass spectra of macerals included in the Atlas part of this volume show the marked differences between these materials. Factor analysis (see Section 6.6.2) of the pyrolysis mass spectra of a series of diagenetically different humic coals (same input materials) revealed that the main factor calculated represented a series of alkyl-substituted phenols, indanes, indenes and benzofurans. Although this set of aromatic fragments cannot simply be ascribed to one particular macromolecular component of the coals, the score of this factor is strongly correlated with the coal rank, i.e. the degree of coalification (ref. 73). Also other chemical features of coal, e.g. the degree of aromaticity or unsaturation, and the presence of sulphur- or oxygen-containing moieties - important factors in industrial coal processing - can be monitored by Py-MS (ref. 98). Altogether, Py-MS appears to be rapidly evolving into an important tool for coal characterisation.

Applications of Py-MS to the characterisation and structural analysis of oil shales and their kerogens have been reported by Maters et al. (ref. 52) and Wojcik et al. (ref. 197) employing the Curie-point and other pyrolysis methods. Different approaches, based on Py-GC/MS and selected ion monitoring have been reported by Sol 1i et al. (refs. 198 - 199), Larter et al. (ref. 200) and Van de Meent et al. (ref. 201). Figure 52 shows the pyrolysis mass spectra of kerogens from three different oil shales, namely Green River shale, Tasmanite and Messel shale. In spite of considerable age difference, the Tasmanite kerogen (250 million years) closely resembles the Green River shale kerogen (50 million years). Whereas Tasmanite and (probably) Green River shale are primarily of algal origin (ref. 52), Messel shale was deposited 50 million years ago in a lacustrine environment and contains considerable amounts of plant residues (ref. 52). The spectrum of Messel shale differs from the other two shales in that it shows the presence of phenolic series typical of lignin, e.g., at m/z 124, 138, 150 and 164. The presence of such methoxylated phenols was confirmed by Maters et al. (ref. 52) using Py-GC/MS techniques. A more detailed inspection of the pyrolysis mass spectra of Tasmanite and Green River shale kerogen shows the

Figure 52. Pyrolysis mass spectra of kerogens from three different oil shales. Note the strong similarity between patterns of Tasmanite (algal) kerogen and of Green River shale kerogen. Further note typical "lignin" series (m/z 94, 108, 124, 138, 150 and 164) in Messel kerogen. Conditions: samples 20 yg; Tc 610°C; Egl 15 eV.

Figure 52. Pyrolysis mass spectra of kerogens from three different oil shales. Note the strong similarity between patterns of Tasmanite (algal) kerogen and of Green River shale kerogen. Further note typical "lignin" series (m/z 94, 108, 124, 138, 150 and 164) in Messel kerogen. Conditions: samples 20 yg; Tc 610°C; Egl 15 eV.

pyrolysates to be mainly composed of aliphatic hydrocarbons exhibiting varying degrees of unsaturation. Apart from small ammonia peaks (m/z 17),no strong nitrogen-containing ion series appear to be present. Marked sulphur-containing ions at m/z 34 (H2S), 48 (CHjSH) and 64 (S02 and/or S9) point to the marine origin of the samples. All of these conclusions, which can be reached by direct inspection of the pyrolysis mass spectrum, confirm the currently held views about the chemical structure of algal kerogens (ref. 202). Moreover, Py-MS can sometimes be applied directly to the whole shale samples without the need for elaborate preparation of kerogens, since spectra obtained from the whole shales may closely match the kerogen spectra (ref. 52).

Whereas the above discussed results show the potential importance of Py-MS techniques for the characterisation of geopolymers of interest, Py-MS techniques have also been applied to more fundamental problems in biogeochemistry. Van der Meide et al. (ref. 203) have reported the use of Curie-point Py-MS for structural studies on organic fractions from fossil Nautilus shells. It would also be interesting to compare fingerprints of well-defined plant remains preserved in coal seams. In spite of the extensive chemical transformation, characteristic differences might still be found. Such differences could be of potential use in palaeotaxonomy. In this context, the Py-MS (and Py-GC/MS) studies of Schenck et al. on differentiation between pollen and spores of different origins (ref. 74) as well as between defined entities within the kerogen matrix should be mentioned.

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