Maceral exinitic

For several years the structural features of a vitrinite (83.9%C) have been intensively studied. The two macerals, exinite and micrinite, which accompany the above mentioned vitrinite in the dull coal were also examined. 

The size and distribution of pores and the size, distribution, and identity of minerals in coal specimens from an eastern Kentucky splint coal and the Illinois No. 6 coal seam were determined by means of transmission electron microscopy (TEM) and analytical electron microscopy (AEM). The observed porosity varies with the macerals such that the finest pores (<2-5 nm) are located in vitrinite, with a broad range of coarser porosity (40-500 nm) associated with the macerals exinite and inertinite. Elemental analyses, for elements of atomic number 11 or greater, in conjunction with selected area diffraction (SAD) experiments served to identify the source of the titanium observed in the granular material as the mineral rutile. Only sulfur could be de-tected in the other coal macerals. Dark-field microscopy is introduced as a means for determining the domain size of the coal macerals. This method should prove useful in the determination of the molecular structure of coal. 

In Figure 9 the vitrinite + exinite content and the reactive maceral content, as determined by ISCOR, are plotted against the total conversion for the hot-rod technique. Figure 10 plots the same information for the autoclave results. 

Figure 9. Percentage conversion against vitrinite + exinite (%) and total reactive macerals (X) (hot rod mode) ( 1)...

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. 

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). 

Of the three major groups of petrographic constituents (termed macerals see appended note), vitrinites and exinites ... 

Similar reflectances of some of the macerals (especially exinite and vitri-nite) in standard oil of n = 1.515 caused difficulties of positive identification. To circumvent this problem, an index oil adjusted to n = 1.60 was compounded from 1-bromonaphtnalene and cedarwood oil. The mixture provided sufficient differences in reflectivity between macerals for meaningful quantification. 

Apart from the exinite and micrinite, all the other coal material in this section is vitrinite and would be counted as such in a maceral analysis. These macerals were identified not only from their form, which is often characteristic, but by direct comparison of the light-microscope picture of the facet from which the ultrathin section was cut (I). By using this technique, each maceral occurrence of sufficient size could be positively identified. 

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. 

With increasing rank, the differences between macerals become progressively smaller in electron as in light microscopy. Exinite in particular becomes difficult to distinguish in medium volatile coals, and could not be positively identified in the electron micrographs of low volatile bituminous coals so far examined. Similarly, the laminate structure of vitrinite described above could not be observed in low volatile bituminous coals. 

Separating the three macerals from the dull coal was difficult. The petro-graphical purity of the exinite is 86% and that of the micrinite 94%. For both macerals, vitrinite is the main impurity. Since the vitrinite has a petrographi-cal purity of 99%, it is not difficult to calculate the values for the pure exinite and pure micrinite from the experimental data on the highly enriched maceral fractions. All values reported in the tables are corrected ones. Table I summarizes the results of elementary analysis (maf) and the percentage of volatile matter. 

From the possible ranges for /. (exinite 0.50-0.66, vitrinite 0.64-0.81, micrinite 0.81-0.91) it follows definitely that the exinite possesses the smallest and the micrinite the highest aromaticity because there is no overlapping of the / intervals of the three macerals. 

Peter H. Given Whereas Tschamler and Fuks, and Peover studied more or less pure vitrinites, Mazumdar apparently worked with whole coals. Moreover, Indian coals, being from Gondwanaland strata, are most probably of very different petrographic composition compared with European and North American coals (rich in exinites and inert macerals See p. 284). Quite apart from the question whether sulfur dehydrogenation really is free of side reactions, there may well be a spread of data at any level or rank because of petrographic differences. 

Samples Studied. From British Seams. The suite of samples was collected and separated by the Coal Survey of the National Coal Board under the direction of Dr. G. W. Fenton, and the authors are indebted to Dr. Fenton for the gift of the samples. The suite consisted of the vitrinites, spore-rich exinites, fusinites and, in one case, the micrinite from five British coal seams of Carboniferous age together with the vitrinites from two coals of higher rank from which it was impracticable to separate the other macerals. The exinites were separated by float-and-sink methods from selected black durain bands, as also... 

Results on Unheated Samples. The results obtained in Southampton for the set of British samples are shown in Figures 2 and 3. In Figure 2 the spin concentration of each maceral is plotted against the carbon content (daf) of the associated vitrinite, and the points for each set of macerals from one coal are joined by a vertical line. It can be seen that the vitrinite series forms a well-defined narrow band which curves upwards sharply at about 90% carbon, and the data resemble closely those presented earlier by Austen and Ingram for whole coals. The values of exinites form a wider, approximately horizontal band lying a little below the vitrinite band, while the fusinite data appear to vary at random but lie consistently well above the vitrinite band and are appreciably higher than vitrinites of the same carbon content (90-92%) would be. 

Marie-Therese Mackowsky I would like to make a suggestion. In Germany, France, Belgium, and Holland we have a so-called central store for pure macerals. This is the laboratory of Dr. Kroger. Consequently, we have a maceral bank, and we can ask Prof. Kroger to send us a few grams of vitrinite, exinite, or micrinite. Perhaps you could have the same here, located perhaps at Pennsylvania State University. 

The composition of the volatile matter evolved from coal is, of course, substantially different for the different ranks of coal, and the proportion of incombustible gases increases as the coal rank decreases. Furthermore, in macerals isolated from any one particular coal, the volatile matter content decreases in a specific order thus, exinite produces more volatile matter than vitrinite, which, in turn, yields more volatile matter than inertinite. 

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. 

Given and coworkers studying the "British Macerals" took more of an organic chemist s approach to characterization. The macerals were subjected to solvent extraction, lithium reduction, hydroxyl determination, oxidation, and reaction with various reagents. N-bromosuccinimide (NBS) was used to bromin-ate aliphatic carbons which in the case for four macerals from an Aldwarke Silkstone coal yielded per 100 carbon atoms the following distribution of hydrogen which is replaced by bromine (61) vitrinite 16, exinite 25 1/2, micrinite 12, and fusinite... 

These values were similar to those obtained by the catalytic dehydrogenation (62) of hvA bituminous coal macerals which yielded in atoms of hydrogen per 100 carbons vitrinite 25, exinite 31, micrinite 18, and fusinite 5. Such results would suggest that vitrinites and exinites should be more reactive in thermal processes and indeed this has been found to be true and will be discussed in the section on reactivity. 

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