Maceral composition

Influence of Maceral Composition. Coals of a similar elemental composition can give different extraction yields. 

For example, Beynon and Cwm coals when digested in anthracene oil give extraction yields of 68% and 47% respectively. This variation can be explained by reference to the maceral composition of the coals. Beynon coal contains a lower concentration of inertinite than the Cwm coal (Table V). In experiments where relatively pure samples of petrographic species were digested in anthracene oil, exinite and vitrinite were shown to be highly soluble, whilst in comparison the inertinite was almost completely insoluble. Similar variations in reactivity of macerals have been reported from studies of solubility in pure organic solvents (1(3). 

Coal Total 1 extraction yield (%) Maceral Composition (%) ... 

A system of classifying coals for solvent extraction, based upon the extent of extraction when using anthracene oil and phenanthrene as solvents has been developed. The reactivity of the coals can be conveniently presented by superimposing the results on Seyler s coal chart. The effects of variations in maceral composition are also discussed. 

Changes In nuclear magnetic resonance measurements of an extensive suite of Australian coals on heating and exposure to pyridine are used to elucidate the molecular conformation of coal macerals Two types of fusible material are Identified In these coals One Is associated with llptlnltes of all ranks and Is typified by fusion commencing at temperatures below 475 K. The other Is associated with vltrlnltes and some Inertlnltes of bituminous coals only and Is characterized by a sharp onset of fusion at temperatures above 625 K. The temperature of onset of fusion Increases with rank for both types The effect of pyridine on the molecular stability of bituminous coals at ambient conditions Is strongly dependent on maceral composition at 86% C and on rank at higher carbon contents ... 

A two-parameter linear regression of AMpyr with both carbon and vitrinlte content for all coals with 86-90 %C that were soaked in pyridine shows that vitrinlte content does not contribute significantly to the correlation and hence that maceral composition is of minor importance compared to rank in determining the ability of pyridine to destabilize higher rank bituminous coals. 

Table I. Maceral Composition of Upper Freeport Coal...

Petrographic continuity of layers may reflect widespread simultaneous deposition of a given maceral composition. If this is true, it is probable that physical and chemical aspects of the peat swamp are more significant factors than local florisbc similarities in establishing the organic composition of the layer. 

The studies carried out consist of the megascopic description of the master columns study of thin sections for maceral assessment, determination of maceral composition on polished blocks in reflected light, determination of mean maximum reflectance values on polished pellets, proximate analyses of selected petrographic zones, hot stage studies on vitrinoids to determine the thermal behavior at various temperatures, electron microprobe and spectrochemical studies of selected zones to determine the nature of ash forming elements, analyses of certain zones petrographically important to determine the variation of total carbon, and hydrogen and microhardness determinations on certain macerals. 

Figure 1. Maceral compositions in size fractions of medium volatile coal...

Figure 2. Triangular diagram showing maceral compositions of microlithotypes...

Crowley, S.S., Warwick, P.D., Ruppert, L.F. and Pontolillo, J. (1997) The origin and distribution of HAPs elements in relation to maceral composition of the Al lignite bed (Paleocene, Calvert Bluff Formation, Wilcox Group), Calvert mine area, east-central Texas. International Journal of Coal Geology, 34, 327-43. 

Coal reflectance (ASTM D-2798) is very useful because it indicates several important properties of coal, including determination of the maceral composition of coal, which, in turn, is helpful for the prediction of behavior in processing (Davis, 1978 Davis et al., 1991). Coal reflectance is determined by the relative degree to which a beam of polarized light is reflected from a polished coal surface that has been prepared according to a standard procedure (ASTM D-2797). Samples prepared by this practice are used for microscopical determination of the reflectance of the organic components in a polished specimen of coal (ASTM D-2798) as well as the volume percent of physical components of coal (ASTM D-2799). 

Table I. Elemental Analysis and Maceral Composition of Coal PSOC-2 and PSOC-858 Separated by Density Gradient Centrifugation Techniques...

Coal lithotypes are megascopically recognizable components of coal. Several nomenclatures have been used to identify the lithotypes [see Damberger et al. (54) for a review of several common classifications]. Coal lithotypes have fairly distinct maceral compositions, which originate from different combinations of plant materials and evolve along somewhat different paths during coalification. 

No correlation was established between the maceral composition and the reactivity behaviour of the cokes (17). 

Recent years have seen vast experimentation with many different process designs for the liquefaction of coals. The degree of coal conversion and composition of the product oil vary with both the coal rank, maceral composition, mineral matter content, and conversion process. Whereas much attention has been focused on the separation and characterization of the product oil by chromatographic and spectroscopic means, less work has been done on the unconverted or process altered residues from liquefaction processes. Although many of the processes do incorporate some sort of bottoms processing , other possible uses of these residues include road materials, carbon electrodes, coal gasification feedstocks, and as direct combustion fuels. Recently, coal conversion by-products have been used as raw materials in the synthesis of thermosetting polyesters. ... 

Liptinites generally make up about 5%-15% of most North American coals. They are usually more abundant in the Appalachian coals than any other US coals except cannel and boghead types where they dominate. At a reflectance of 1.35-1.40, most of the liptinite macerals disappear from coal. Cannel and boghead coals are petrographically distinguished from humic coals by both their maceral composition and texture. They have an abundance of liptinite macerals (sporinite in can-nels and alginite in boghead coal) and a relative low level of vitrinite and inertinite macerals. 

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. 

Coal reflectance is important in aiding the determination of the maceral composition of coal which, in turn, is helpful for the prediction of behavior in processing (Davis et al., 1991) (Chapter 4). For example,... 

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