Sporinite separation

Successfully applying the method used by Fenton to prepare his concentrates depends upon two factors. First, there must be adequate density differences between the macerals in the sample, and second, there must be an initially high concentration of the required maceral. In attempting to separate either resinite or cutinite from sporinite of the same coal, neither of these conditions can be fulfilled, at least when the coal is of bituminous rank or higher. If, however, samples on a semi microscale are acceptable, it is possible to prepare concentrates of resinites of satisfactory purity from bituminous coals by simple mechanical means. The method has been described by Murchison and Jones (17) and mainly involves picking with fine probes on differently prepared surfaces of coal under a stereoscopic microscope. Resinites from lignites pose less of a problem because their occurrence in fairly substantial lumps is quite common these and fossil resins such as kauri gum and amber usually can be prepared to a purity of almost 100% with ease. 

Our recent development of a new procedure for the density separation of macerals offers a method for obtaining high resolution separation of the three maceral groups exinite, vitrinite, and inertinite, and can further resolve individual maceral types within these macerals groups, e.g., sporinite from alginite in the exinite group (1,2). The procedure... 

Figure 1. This bar graph shows the variation in the m/z = 108 peak components from Py-MS for a series of macerals. The sporinite and vitrinite are separated from the Brazil Block seam coal.

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. 

Although many of the oxidation products are common to all of the samples analysed, their distribution varies considerably from sample to sample. In addition, there are some oxidation products that appear exclusively in the FID traces of some samples. For instance, there are compounds in sporinite and inertinite samples which do not appear in the FID trace obtained for their parent floated coal. The absence of these compounds in the FID traces of the floated coals is explained by the presence of the more abundant maceral vitrinite, the oxidation products of which either swamp or dilute those from the lesser macerals, making their detection very difficult. Here we see how maceral separation is important for the characterization, not only of the individual macerals themselves, but of the whole coal. Observation of sulfur constituents that are unique to minor macerals components may be difficult to detect during the analysis of a whole coal, but are easily observed during analysis of individual macerals. 

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