Macerals groups

A number of subdivisions of the maceral groups have been developed and documented by the International Commission on Coal Petrology (14). Table 1 Usts the Stopes-Heeden classification of higher rank coals. Periodic revisions include descriptions of the macerals, submacerals, morphology, physical properties, and chemical characteristics. Theories on the mode of formation of the macerals and their significance in commercial appUcations are also included of Reference 14. 

Table 1. Stopes-Heerlen Classification of Maceral Groups, Macerals, and Submacerals of Higher Rank Coals ...

The elemental composition of the three maceral groups varies. The vitrinite, which frequently is about 85% of the sample in the United States, is similar to the patent coal. The liptinites are richer in hydrogen, whereas the inertinites are relatively deficient in hydrogen and richer in carbon. The liptinites also contain more aliphatic materials the inertinites are richer in aromatics. The term inertinite refers to the relative chemical inertness of this material, making it especially undesirable for Hquefaction processes because it tends to accumulate in recycled feedstock streams. 

Macadam color difference scale, 7 321 MacAdams ellipses, 7 322 MacCoull equation, 25 207 Mace, 23 155, 168 Maceral groups, 6 706... 

By applying this analysis at discrete 10 K temperature intervals to the NMR thermal analysis data for the 102 coals (subdivided into brown coals (<75% C), lower rank (80-85% C) and higher rank (85-90% C) bituminous coals), regression coefficients could be obtained as functions of temperature and hence the average 2T of the three maceral groups were generated (Figures 3-... 

The relative degree of denseness (i.e., opacity to electrons) of the macerals is exinite least dense, vitrinite intermediate, and inertinite most dense of the coal maceral groups. That is, the light/dark relations are similar to those observed in the usual thin sections examined in the light microscope. 

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. 

Exinite microscopic coal constituent (maceral) or maceral group containing spores and cuticles. Appears dark gray in reflected light. See also Maceral. 

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. 

In the first half of this introductory chapter the maceral concept has been discussed and the main maceral groups and their important maceral types described. Emphasis has been placed on in situ characterization techniques which rely mostly on microscopy. The rest of this chapter will examine other techniques used for chemical characterization and examine the reactivity of coal macerals in thermal processes. The availability of separated maceral concentrates was a necessary component of the studies which will be described. 

The preparation of maceral concentrates for study has been achieved by one of two approaches, either by hand picking or by a variety of techniques which exploit the variation in density between the various maceral groups. The first level of hand picking is the judicious sampling of lithotypes. This term is used to identify the various layers found in a coal seam. For humic coals there are four main designations of lithotypes vitrain, clarain, durain, and fusain (42). Vitrain bands are sources of fairly pure vitrinite group macerals while fusinite and semi-fusinite can be obtained from fusain. These are the... 

Figure 2. A van Krevelen plot showing approximate bands for the three main maceral groups.

Free Radicals in Macerals. Electron spin resonance (ESR) has been used to study carbon free radicals in coals, and to some extent, separated macerals. The technique provides information on radical density and the environment of the radicals. The resonance position, termed the g-value, is dependent on the structure of the molecule which contains the free electron. The line width is also sensitive to the environment of the unpaired electron. In an early study, Kroger (71) reported that the spin concentration varied between maceral groups with liptinite < vitrinite inertinite. For this limited set of samples the spin concentration increases with rank for liptinites and vitrinites and decreases for the micrinite samples. On the other hand, van Krevelen (72) found the same general results except... 

Another rapid technique for characterizing non-volatile materials which has been applied to coal macerals is pyrolysis mass spectrometry (Py-MS) (82-84). The evaluation of the complex data produced by this technique has been aided by the use of statistical analysis. Homologous series of molecules can be identified and variation between the various maceral groups is quite evident. 

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... 

What do these variations represent There are a number of factors which can be invoked to explain the changes observed. Each of the three major maceral groups is composed... 

The fact that not only heterogeneity due to maceral groups, but some heterogeneity due to variations within maceral groups can be reduced implies density gradient... 

We wish to report data on a series of whole coals and coal macerals using conventional CP/MAS, dipolar dephasing, and 2-D dipolar dephasing techniques. These data provide a wealth of new structural information and demonstrate that multiple pulse and 2-D spectroscopic techniques can be utilized on complex carbonaceous materials. We also report data obtained on maceral samples separated by the density gradient centrifugation method which separates coal maceral groups according to density. 

The maceral groups from these coals were separated by the density gradient centrifugation (DGC) technique described by Dyrkacz... 

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