Vitrinite structure

H/C = atomic hydrogen-to-carbon ratio V = vitrinite content of coal VM volatile matter St = total sulfur TRM = total reactive macerals The adequacies of these reactivity correlations, expressed as a percentage of the total variation in the data set explained by the model, were 80.0%, 79.2%, and 47.5% respectively. A later paper in the series (21) concentrated on the development of reactivity correlations for a set of 26 high volatile bituminous coals with high sulfur contents, and extended the models previously developed in include analyses of the liquefaction products and coal structural features. These structural features included the usual... 

The above models are representative of the active macerals, particularly vitrinite. Inert macerals, such as fusinite and micrinite, are believed to have large aromatic planar structures with fewer substituents (14) and behave similar to chars. 

Since the work reported by McCartney et al. (9), ultrathin sections of other, more heterogeneous components and mixtures of components of coals of different rank have been prepared and observed. Procedures for minimizing artifacts have been learned and followed, and experience in observation has led to avoiding obvious faults. These sections were often not as large and continuous as those of homogeneous vitrinites, but adequate areas were available for electron microscopy. Observations of these various components revealed ultrafine structures of different size and form. Some of the structures can be correlated with those deduced from other direct or indirect study techniques others are unfamiliar and novel, and suggested interpretations are tentative. 

The physical or petrographic components of coal are defined or described in various ways. In one system, which depends on microscopic observation, the principal components are called exinite, vitrinite, micrinite, and fusinite. Transparency of these in a thin section decreases in that order, whereas reflectance from polished surface increases in the same order. Vitrinite, the major component of most coals, occurs in bands or strands and is usually uniform in appearance, though sometimes shows cell structure exinite consists of the remains of plant spores, pollen, and cuticles with characteristic shape micrinite occurs in very fine granular form or massive structureless, irregular form fusinite shows characteristic fibrous, cellular structure. Semifusinite is transitional between vitrinite and fusinite. On a macroscopic scale, vitrain and... 

Mr. McCartney. It would be possible for the 50-A. granular structure of the vitrinite specimen of Figure 12 to have been derived from the colloidal structure of humic acids. However, the similar structures of Figures 10 and 11 in exinite and fusain could hardly be ascribed to such an origin. 

In general, details of cell structure in vitrinite are distinguished only with great difficulty in ultrathin sections in the electron microscope, probably because of insufficient contrast between cell parts. If cell spaces are filled with another component the cellular structure becomes evident. 

Examination of ultrathin tactions of coal in tko aloctron microscope hat revealed that one type of vitrinite (vitrinite A) it homogeneous, while the remaining vitrinite (vitrinite B) it a two-component material, the components having similar properties to vitrinite A and exinite, respectively. The material similar to exinite occurs in sheets no more than 1000 A. thick and is responsible for the lower reflectance and higher volatile matter yield of vitrinite B. Exinite, micrinite, and semifusinite have been identified in ultrathin sections. By using a technique of impregnation with a lead salt the ultrafine pore structure of vitrinite has been made visible. 

Figure 1. Vitrinite containing thin sheet-like structures of material similar to exinite in many of its properties. X 6750...

Figure 3. A band of exinite showing fine structure. The associated vitrinite is almost entirely homogeneous. X 4725...

The vitrinite without any sheets appears to correspond to what Brown, Cook, and Taylor (2) have called vitrinite A that with sheets appears to correspond to vitrinite B. The existence of this kind of laminar structure helps to explain the observation that vitrinite B has a higher volatile matter yield than vitrinite A although some of the coking properties of the two vitrinite types seem fairly similar. Many of the coking properties in fact appear to be primarily related to the matrix vitrinite. 

Figure 5. Contact between semifusinite (showing cellular structure) and vitrinite. This junction appeared to be transitional in the light microscope but at this magnification appears sharp. X 4390...

Semifusinites behave like micrinites of similar reflectance. Examining several specimens by electron microscopy, where light microscopy had shown apparently gradual transitions from vitrinite to semifusinite, suggested that the transition was at least partly step-wise in nature (Figure 5). In some semifusinite, the actual cell walls could be observed within the generally cellular structure (Figure 5). 

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. 

Figure 6. Replica of a high volatile coal (polished suiface) showing sheet-like structures in vitrinite. X 4050...

It was considered likely that any fine structure present might not be obvious owing to lack of contrast. In an attempt to reveal any structures present, samples of vitrinite were evacuated at 10" mm. Hg for several days and then impregnated with a saturated aqueous solution of lead acetate. The solution was allowed to dry over a period of several days and then some of the vitrinite was freed from the encrusting lead acetate, crushed finely, and dispersed on a carbon-collodion filmed grid. 

Dr. Taylor. Much of our vitrinite A would be telinite, and much of our vitrinite B would be collinite. However, we have found great difficulty in using the concepts of collinite and telinite because whether or not one sees cell structure to some extent depends upon the techniques used. 

Dr. Taylor. The vitrinite in vitrite layers was mostly either featureless or showed traces of cell wall structures similar to those in ordinary thin sections. Some vitrinite of this type is to be seen in the photographs shown (see Figure 3). 

Little comment can be made about the hydrogen-bonded OH groups that absorb close to 3300 cm."1. It is unlikely, however, within the rank range of resinites covered here that much variation in the intensity of this absorption would be recorded. The broad region of absorption between 1100 and 1300 cm."1 common to vitrinite and sporinite spectra is also found in the resinite spectra. The peak at 1270 cm. 1 almost certainly corresponds to the 1250 cm."1 band assigned by other workers to hydrogen-bonded phenolic structures. Fol-... 

Aliphatic structures are still of major importance in the second group of resinites, those of the bituminous coals, but aromatic structures are present in significant amounts. The spectra of these resinites display the type of absorption pattern that has come to be associated with other coal macerals, particularly the sporinites and to a large extent the vitrinites. This pattern is established in the resinites of the high volatile bituminous coals. Furthermore, resinites of this group are reactive during carbonization and oxidation processes in which their behavior parallels that of similarly affected vitrinites of equivalent rank. 

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. 

Since the structural parameter H.i/C i cannot be determined experimentally, only particular f. values can be derived for example, the theoretically highest fm value follows from the assumption that H i/C i = 3, which means that the entire aliphatic portion consists of CH3 groups. A more realistic value of fm follows if in Equation 2 H.1/C.1 = 2 (the aliphatic portion consists either only of CH2 groups or of the same number CHa and CH groups with or without CH2 groups) is used. These two theoretical but meaningful / values are 0.92 and 0.88 for the micrinite, 0.84 and 0.77 for the vitrinite, and 0.75 and 0.82 for the exinite. 

The values in Table VII show that 12 nonaromatic rings should be present for nine mean structural units in the case of exinite, 10 in the case of vitrinite, and 16 in the case of micrinite. Since all faiIt -Rnnr) values are higher than the highest ones obtained from the aliphatic group distribution (see Table IV), all samples must contain nonaromatic rings even if the most probable / values... 

Table VII. Mean Number of Nonaromatic Rings, Rn r per Structural Unit and f

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