Maceral in coal

The refractive index of coal can be determined by comparing the reflectance in air with that in cedar oil. A standard test method (ASTM D-2798) covers the microscopic determination of both the mean maximum reflectance and the mean random reflectance measured in oil of polished surfaces of vitrinite and other macerals in coal ranging in rank from lignite to anthracite. This test method can be used to determine the reflectance of other macerals. For vitrinite (various coals), the refractive index usually falls within the range 1.68 (58% carbon coal) to 2.02 (96% carbon coal). 

Determine amount of ash, carbon, hydrogen, nitrogen, oxygen, and sulfur Identify products given off as gases or vapors Determine kinds and amounts of macerals in coal... 

Table 34. Petrologic components (macerals) in coal and then-groupings...

Macerals. Coal parts derived from different plant parts, are referred to as macerals (13). The maceral names end in "-inite" as do the mineral forms of rocks. The most abundant (about 85%) maceral in U.S. coal is vitrinite, derived from the woody tissues of plants. Another maceral, called liptinite, is derived from the waxy parts of spores and poUen, or algal remains. The liptinite macerals fluoresce under blue light permitting a subdivision based on fluorescence. A third maceral, inertinite, is thought to be derived from oxidized material or fossilized charcoal remnants of early forest fires. 

The macerals in lower rank coals, eg, lignite and subbiturninous coal, are more complex and have been given a special classification. The term huminite has been appUed to the macerals derived from the humification of lignocellulosic tissues. Huminite is the precursor to the vitrinite observed in... 

There are certainly lithotypes that can be handpicked from European and American coals that are relatively rich in fusinite and semifusinite. However, it is perhaps significant that the mean content of total fusinite + semifusinite in 697 coal samples in the Penn State/DOE Data Base is 8.9%. On the other hand, the content of inertinite macerals in the Permian coals of Gondwana-land is notoriously high and much of this inertinite material consists of semifusinite (5,26,33,34), the concentration of which can be as high as 50% in the whole seam. 

Teichmiiller (39) has indicated that coals formed in saline environments tend to be richer in hydrogen and nitrogen than freshwater coals. She also believes that certain fluorescent macerals may be relatively more abundant in coals formed in more saline conditions in accordance with this view, fluorinite and fluorescent vitrinite appear to be more abundant in coals from Illinois than in those in the Eastern province. 

The reactive role of liptinite macerals in liquefaction has been partially documented (50,68). However, recent work has shown that unaltered sporinite often is encountered in the residues from both batch and continuous liquefaction runs. For example, sporinite was a common component in the residues of a high volatile A bituminous coal after hydrogen-transfer runs at 400° for 30 minutes (70). In spite of the relative unreactivity of the sporinite in this instance, the vitrinite clearly had reacted extensively because vitroplast was the predominant residue component. The dissolution rate of sporinite from some coals, even at 400°C, may be somewhat less than that of vitrinite. 

It is possible to produce some liquid hydrocarbons from most coals during conversion (pyrolysis and hydrogenation/ catalytic and via solvent refining)/ but the yield and hydrogen consumption required to achieve this yield can vary widely from coal to coal. The weight of data in the literature indicate that the liquid hydrocarbons are derived from the so-called reactive maceralS/ i.e. the vitrinites and exinites present (7 8 1 9). Thusf for coals of the same rank the yield of liquids during conversion would be expected to vary with the vitrinite plus exinite contents. This leads to the general question of effect of rank on the response of a vitrinite and on the yield of liquid products and/ in the context of Australian bituminous coals, where semi-fusinite is usually abundant/ of the role of this maceral in conversion. 

Thermal destabilization of the molecular lattice of aromatlc-rlch macerals In bituminous coals at temperatures above 600 K Is associated with their characteristic thermoplasticity (10). The relationship between the extent of this fusion and the molecular properties of the vltrlnlte and Inertlnlte macerals, however. Is not well understood. 

Fusion of the llptlnlte macerals In bituminous coals commences at lower temperatures and reaches a much greater extent than that of the aromatic macerals (Figures 4 and 5). The greater thermal stability Indicated by the much higher fusion temperatures of the bituminous llptlnltes compared to brown coal llptlnltes can be explained In terms of these materials having a more highly crossllnked macromolecular structure than the llptlnltes In the brown coals. This Increase with coallflcatlon could be the consequence of In situ crosslinking of material or the selective loss of llptlnlte fractions that are less crossllnked and therefore less Inherently stable ... 

Two distinct types of fusible material occur in coals. One type is aliphatic-rich and associated with the liptinite macerals and the other is contained in the aromatic-rich macerals and particularly the vltrinites of bituminous coals. 

Nandi Q), in their investigation into the role of inert coal macerals in pulverised fuel... 

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. 

Both groups of spectra show greater complexity than the spectra of resinites from bituminous coals, particularly in the region below 1250 cm. 1 in which numerous but generally weak absorption bands occur. A complete and realistic interpretation within this region would be virtually impossible without considerable chemical study, and it was not the intention of the present investigation to cope with this problem. It was hoped to establish how the absorption pattern of lower rank resinites compared with that of the maceral in bituminous coals and in particular to see what spectral characters were possessed by possible precursors of bituminous coal resinites. 

The chief question of geochemical interest is how the radicals came to be in the macerals in the first place and why the change with rank is as found. Although it has been known for some years that whole coals contain appreciable concentrations of free radicals, this question appears not to have been discussed previously in any general way. Three possible answers suggest themselves. 

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. 

The vitrinitic substances found in coal seams are commonly asserted to be derived from wood or woody tissue. The statement is usually made without any intention of being specific about what is meant by w ood and, in fact, several non-wood tissues are often included intentionally in this broad generalization. It is generally agreed that various different substances are contained in these woody source materials and that several different biochemical, chemical, and physical processes may influence their alteration. In spite of this, our coal research has led many individuals to think of the vitrinites as forming a single maceral series. The coalified w oods in the Brandon lignite... 

Maceral analyses—i.e., coal constituent analyses—were made on polished pellets of the coal samples from 9, 7, and 6 feet from the sill contact. A Leitz Ortholux microscope at approximately 750X magnification was used. At a distance of less than 6 feet from the sill contact it was impossible to distinguish any specific macerals in the coal samples. At 6 feet it was possible to distinguish the macerals, and a ratio of reactives to inerts of 20 80% was found. At 9 feet there was an approximate ratio of 70 30% of reactives to inerts. The bulk of the increase is caused by carbonization of other macerals. 

This volume covers a wide range of fundamental topics in coal maceral science that varies from the biological origin of macerals to their chemical reactivity. Several chapters report novel applications of instrumental techniques for maceral characterization. These new approaches include solid l3C NMR, electron spin resonance, IR spectroscopy, fluorescence microscopy, and mass spectrometry. A recently developed method for maceral separation is also presented many of the new instrumental approaches have been applied to macerals separated by this new method. The contributions in this volume present a sampling of the new directions being taken in the study of coal macerals to further our knowledge of coal petrology and coal chemistry. 

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