Sporinite aromaticities

Aliphatic structures are still of major importance in the second group of resinites, those of the bituminous coals, but aromatic structures are present in significant amounts. The spectra of these resinites display the type of absorption pattern that has come to be associated with other coal macerals, particularly the sporinites and to a large extent the vitrinites. This pattern is established in the resinites of the high volatile bituminous coals. Furthermore, resinites of this group are reactive during carbonization and oxidation processes in which their behavior parallels that of similarly affected vitrinites of equivalent rank. 

Of particular interest in this study is the nature of the non-aromatic structures in the three main maceral groups. It should be noted that the exinites in both the coals separated by float-sink are 90% sporinite. It has been theorized that small molecules, especially the aliphatics, are fairly mobile at some period during the formation of coal (5,6). The studies which support this theory were done on coals that are very rich in exinites and some contained alginite. Two of the coals chosen in the present work (PSOC 828 and 1103) have a more normal distribution of macerals and yet the pyrolysis results indicate that migration of molecules from the exinites to vitrinite and then incorporation into the macromolecular structure might have occurred. 

There was a much larger variation between pyrolysis products volatile fractions for the exinites and vitrinites. The sporinite yielded mostly normal alkanes and alkenes up to approximately C19 with C16 being the most abundant product. The very low molecular weight hydrocarbons such as methane and ethane were not analyzed. Also, benzene and phenol derivatives were found as minor products. The vitrinite products were dominated by aromatics such as alkyl benzenes, alkylnaphthalenes, phenols, and naphthols. The smaller alkane/alkenes were also found. These results are most consistent with what was found in pyrolysis MS of sporinites and vitrinites (5,7). 

The sporinite spectra (Figure 2), while exhibiting broad similarities, are found on careful examination to have subtle differences in both the aliphatic and aromatic regions. In the aliphatic portion of the spectra these differences are associated with variations in the relative amounts of CH3, CH2, and (CH2)n structural moieties. Both spectra exhibit shoulders at 13-15 ppm (terminal methyl region), but the band at 22-24 ppm in the... 

It is interesting that a bituminous coal (Sample 4) gave organic acids qualitatively similar to those of lignite coal see Figure Id). Major identified compounds were p-hydroxybenzoic acid and two isomers of hydroxybenzenedicarboxylic acid, benzene di- and tricarboxylic acids. No ortho or meta isomer of hydroxybenzoic acid was detected. We have found that solvent-extractable hydrocarbons obtained from this raw coal consist mainly of n-alkanes (Cjj to 3 ). This is quite different from other results which showed that aromatic hydrocarbons were the major solvent-extractable material of several bituminous and anthracite coals (21). Indeed, petrographic analysis shows that this coal has a high content of sporinite (14.3 wt %) and a low content of vitrinite (30.2 wt %) (33). 

The purpose of many analyses on kerogens is related to their typing, which is very useful for petroleum exploration purposes [39]. As an example, the ratio xylene/octene from the pyrogram of different kerogens can be related to their rank, as shown in Figure 14.4.2 [40]. The presence of aromatic hydrocarbons in the pyrolysate of vitrinites is very high (xylene/octene up to 50), the alginites have low aromaticity, while sporinites have intermediate levels. 

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