Whole coals characterization

Peter H. Given I should like to remark on model structures for coals. Chemists have often been criticized for offering information about coal structure based on experiments with whole coals or with imperfectly characterized materials. Even when one works with what is believed to be reasonably pure materials, there may be questions raised. 

Scanning electron microscopy with an energy-dispersive x-ray system accessory has been used to identify the composition and nature of minerals in coals and to determine the associations of minerals with each other. Examinations can be made on samples resulting from ashing techniques or whole coal. With this technique it is possible to identify the elemental components and deduce the mineral types present in coal samples. Computerized systems to evaluate scanning electron microscopy images have been developed and are useful in characterizing the minerals in coal mine dusts and in coal. 

Part of this data in Table II is a series of British maceral concentrates. The Woolley Wheatly Lime sample is 93% fusinite while the Teversal Dunsil concentrate is 80% semifusinite with 13% fusinite. The Aldwarke Silkstone sample contains 43% semifu-sinite and 43% fusinite. The petrographic analysis of PSOC-2 reveals nearly equivalent amounts of fusinite, semifusinite, micrinite, and macrinite (6.8, 8.1, 7.5 and 8.5% respectively in the whole coal) while PSOC-858 contains primarily semifusinite as the inertinite. The differences in faH values for these iner-tinite samples are greater than the experimental error and these differences suggest that NMR techniques may be useful in characterizing the chemical structural differences between inertinite macerals. 

Extrapolating the data from these analyses to characterize the whole coal can be very misleading. 

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. 

Only through maceral separation can some of the sulfur compounds be detected. Maceral separation is therefore to be considered essential not only for the characterization of individual macerals but the characterization of whole coals as well. 

Solvent Fractionation. To facilitate later structural analysis, we separated the coal into structural types by solvent fractionation. Some other workers using the phenol depolymerization method to solubilize coal have used gas chroma-tography/mass spectroscopy (GC/MS) techniques to identify individual compounds (11, 13). However, with material containing large amounts of phenol and other polar groups, elaborate preparation and separation schemes have to be used to avoid contamination of the chromatography columns. As the emphasis of the present work was on structural characterization of the whole coal rather than on detailed examination of small parts of it in order to elucidate the chemistry of the phenolation reaction, we used the relatively simple scheme shown in Figure 1. 

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