Vitrinite analysis

Seam correlations, measurements of rank and geologic history, interpretation of petroleum (qv) formation with coal deposits, prediction of coke properties, and detection of coal oxidation can be deterrnined from petrographic analysis. Constituents of seams can be observed over considerable distances, permitting the correlation of seam profiles in coal basins. Measurements of vitrinite reflectance within a seam permit mapping of variations in thermal and tectonic histories. Figure 2 indicates the relationship of vitrinite reflectance to maximum temperatures and effective heating time in the seam (11,15). 

Analysis of the results presented in Figures 2 and 4 appears to indicate that hydrogenation of the vitrinite is also accompanied by polymerization (see pyridine extract, Figure 4). If this can be confirmed, it would be worth investigating whether it involves specific fractions in the original vitrinite or has a random character. Solvolysis of different molecular weight fractions of a non-reductively alkylated vitrinite (or coal) may furnish some insight. 

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). 

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. 

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. 

Fluidity data were determined by the Gieseler apparatus on the 16 size fractions of the medium volatile coal. The values obtained were relatively low, ranging from 8 to 81 dial divisions per minute. An attempt was made to correlate these results with petrographic data. Some of the possible relations examined are shown in Figure 4. A plot of the maceral vitrinite against fluidity shows considerable scatter as does a plot of the ash content vs. fluidity. The ash content was determined by proximate analysis (see Table I) and is included here for comparison. 

Cody, G. D., Ade, H., Wirick, S., Mitchell, G. D., and Davis, A. (1998). Determination of chemical-structural changes in vitrinite accompaying luminescence alteration using C-NEXAFS analysis. Org. Geochem. 28,441 455. 

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-... 

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-... 

Aliphatic stretching region in vitrinite, rotated matrix of factor loadings for components analysis of FTIR absorption bands, 1l4t... 

Although many of the oxidation products are common to all of the samples analysed, their distribution varies considerably from sample to sample. In addition, there are some oxidation products that appear exclusively in the FID traces of some samples. For instance, there are compounds in sporinite and inertinite samples which do not appear in the FID trace obtained for their parent floated coal. The absence of these compounds in the FID traces of the floated coals is explained by the presence of the more abundant maceral vitrinite, the oxidation products of which either swamp or dilute those from the lesser macerals, making their detection very difficult. Here we see how maceral separation is important for the characterization, not only of the individual macerals themselves, but of the whole coal. Observation of sulfur constituents that are unique to minor macerals components may be difficult to detect during the analysis of a whole coal, but are easily observed during analysis of individual macerals. 

The vitrinite samples from the Lower Kittaning seam were run as received. The chemical analysis is given in Table III. 

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