Vitrinitic macerals

The circular black region is a resin filled devolatilization pore surrounded by bitumen semicoke. Fused vitrinite is the bright region with very little texture. The photomicrograph suggests that neither the bitumen or the plastic coal are mutually soluble and the presence of bitumen does not interfere strongly with the fusion of vitrinite macerals. 

There has been available (or some years unarguable evidence that each of the major macerals groups has a distinct set of structural characteristics, and that the major macerals in any one coal do differ materially in chemical structure from each other. We must therefore admit that chemical structures alleged to represent whole coals are futile, and that basic chemical research should use single macerals in as pure a state as possible. On the other hand, some believe that pure vitrinite macerals at least can be represented usefully by a model structure. 

Vitrinite maceral and maceral group composing all or almost all of the villain and like material occurring in attrital coal as the component of reflectance intermediate between those of exinite and inertinite. 

The technique also yields quantitative spectra that are characteristic of both the individual maceral type and the rank of the coal. It is now also well established that all of the liptinite macerals (coal components derived from the resinous and waxy plant material) and many of the vitrinite macerals (coal components derived from woody tissue of plants) will fluoresce, and that some recently discovered liptinite macerals can only be identified by their fluorescence properties. 

Figure 2. The ESR absorption of a vitrinite maceral sample from PSOC 297 illustrates the broad, fine structure free character of these spectra.

The first such study was reported by Hsieh and Wert (10). Measurements on a thinned vitrinite maceral of an Illinois 6 coal at a spacing of... 

We have employed CP/MAS techniques for characterizing two sets of coal macerals. In the first set, we examined eight maceral samples (two alginites, two sporinites, three vitrinites and one fusinite) of Carboniferous and Permo-Carboniferous age which have been previously reported (14). We now compare this work with a set of six hand picked vitrinite macerals from the Lower Kittaning seam. 

Type III kerogen is essentially formed from vascular plants and contains much identifiable plant debris, so vitrinite macerals predominate. Sulphur-rich brown coals can be formed, which have been described as type III—S kerogen (Sinninghe Damste et al. 1992). 

The predominant aliphatic units in type III kerogen are small chains (mostly methyl and propyl), primarily derived from lignin residues in vitrinite macerals, and so hydrocarbon gases, particularly methane, are the main petroleum products. There may be some potential for oil production if cutan and/or suberan has been incorporated into the kerogen. Similarly, there is now... 

Huminite/vitrinite macerals are derived from humic substances, the alteration products of lignin and cellulose. Huminite refers to macerals in lignite and subbituminous rank (see the following) coals (S korovd et al, 2005), and vitrinite to maceral of bituminous and anthracitic ranks. 

Of the three maceral groups, vitrinite is more familiar as the brilliant black bands of coal. Vitrinite macerals are derived from the cell wall material (woody tissue) of plants, which are chemically composed of the polymers, cellulose and lignin. The vitrinite group is the most abundant group and typically makes up 50%-90% of most North American coals. However, most Gondwanaland coals and some western Canadian coals are vitrinite poor —the inertinite macerals dominate in these coals. 

The major petrographic feature of the liptinite group of macerals is that they all have a reflectance that is lower than the vitrinite macerals in the same coal. This group of macerals is very sensitive to advanced coalification and the exinite macerals begin to disappear in coals of medium-volatile rank and are absent in coals of low-volatile rank. When the exinite macerals are present in a coal, they tend to retain their original plant form and thus they are usually plant fossils phyterals). The phyteral nature of the liptinite macerals is the main basis on which they are classified. 

The FSI or crucible swelling number (CSN), which is a measure of the ino-ease in volume of the coal when it is heated in the absence of air. This test is also used to characterize coals for combustion. The FSI is at least in part a rank-dependent parameter but also depends on the maceral composition of the coal, the vitrinite maceral group being the main contributor to the swelling properties. 

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