Vitrinite aromaticities

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. 

Vitrinite Reflectance. The amount of light reflected from a poHshed plane surface of a coal particle under specified illumination conditions increases with the aromaticity of the sample and the rank of the coal or maceral. Precise measurements of reflectance, usually expressed as a percentage, ate used as an indication of coal rank. 

It has been proposed (17) that the portion of coal which is mobile under liquefaction conditions, contributes to the stabilization of thermally-generated radicals. Thus, coals which are highly fluid or contain large contents of extractable material might be expected to provide hydrogen and thus promote conversion. Collins has reported that vitrinite is a better donor of hydrogen than is Tetralin (20). Our own measurements of the aromatic content and elemental analyses of the coals (16,21) (or coal products) before and after conversion at short time are insufficient to confirm or deny the supposition that coal acts as its own H-donor even at short times. 

In Curie-point Py-LVMS studies of maceral concentrates (22). vitrinitic moieties were shown to be the main source of the hydroxy aromatic components. Thus, the hydroxy aromatic signals observed in Figure 2d appear to be primarily derived from vitrinite-like components by means of pyrolytic processes. Presumably, therefore, the "nonmobile phase", rather than the "mobile phase , is the main source of the phenols observed in TG/MS and Py-MS studies of Pittsburgh 8 coal (9,16). Further support for this conjecture comes from the observation that phenolic products are also observed in Py-MS analysis of pyridine extracts of Pittsburgh 8 coal known to contain colloidal matter whereas the corresponding tetrahydrofuran extracts, free of colloidal material, produced no phenols (21). 

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. 

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. 

It is, however, known that the fa values from Equation 1 must be regarded as being too low because not only the aliphatic part but also small aromatic systems are split off during determination of the volatile matter (II). Furthermore, these fa values make sense only as long as the %V is not too high. This method is, therefore, limited to the vitrinite (/- = 0.75) and micrinite (fa = 0.87). 

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. 

Table V. Values of the Aromatic Substitution Index S.r, depending on aromaticity f and H r/H for an Exinite, Vitrinite, and Micrinite...

Various methods and assumptions give for a vitrinite of 84% C content, values of aromaticity, / , ranging from 0.64 to 0.81 (3). A number of arguments suggest that H.i/C.t should be at least 1.65, which raises the minimum value for / to 0.71. For various reasons (4) we believe 0.77 is the most probable value, which would mean that C.i/C is 0.23. Certainly not all aliphatic carbon is alicyclic, so that C.nc7ci/C must be smaller than C.i/C. Hence we feel that the data of Peover in the above table are unrealistic, but all the other values (including the revised figures of Mazumdar et al. but not... 

In Figure 3 the IR spectrum of a subregion of vitrinite about 0.010 mmz in area is compared with the IR spectrum from an equal area which is within a single megaspore. The two regions of analysis are on the same piece of thin section and they are separated by only about 160 micrometers. The two minute scans of the 15 micrometer thick samples give excellent signal to noise ratios. As described in the results section, these spectra clearly contrast the more aromatic and hydroxyl-... 

Quantitative FTIR data were combined with chemical and petrographic data for the 24 vitrinite concentrates and subjected to bivariate and multivariate statistical analyses in order to identify the effects of coal ification on the aliphatic and aromatic functional groups. 

The components analysis containing vitrinite reflectance is reported in Table IX. Reflectance is split into three components, loading most strongly on component 1. The aromatic bands represented by that at 750 cm-1 show complete dependency with reflect-... 

Statistical analyses were performed on FTIR data from the aliphatic and aromatic regions and selected parameters of coalification for 24 vitrinite concentrates from the Lower Kittanning seam. 

Inertinite radicals have very uniform g values, the magnitude of which suggests association with aromatic molecules. Radical densities can be extremely high (up to 25 x the levels seen in exinites). The linewidths are much narrower than in other maceral types ( l-2 Gauss vs 7 G for exinites and vitrinites), and both widths and shapes depend sensitively on the maceral "history", as reflected in atomic H/C ratios and the density. 

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