Maceration types

In the first half of this introductory chapter the maceral concept has been discussed and the main maceral groups and their important maceral types described. Emphasis has been placed on in situ characterization techniques which rely mostly on microscopy. The rest of this chapter will examine other techniques used for chemical characterization and examine the reactivity of coal macerals in thermal processes. The availability of separated maceral concentrates was a necessary component of the studies which will be described. 

Compared to conventional white-light analysis, fluorescence microscopy reveals a greater number and variety of macerals, as well as, characteristic textures and structures. Although the spectra of fluorescent macerals are broad-peaked and, at this time, not suitable for chemical structure analysis, they are characteristic of maceral types and rank. 

The technique also yields quantitative spectra that are characteristic of both the individual maceral type and the rank of the coal. It is now also well established that all of the liptinite macerals (coal components derived from the resinous and waxy plant material) and many of the vitrinite macerals (coal components derived from woody tissue of plants) will fluoresce, and that some recently discovered liptinite macerals can only be identified by their fluorescence properties. 

Although the characterization of coal macerals on the basis of their fluorescence spectra is a recent innovation, it has already proven to be an excellent fingerprinting tool for the various macerals. In some cases, it is even more sensitive than normal petrographic analysis. The initial results of fluorescence spectral studies show that the various fluorescent macerals in single coals can be statistically discriminated on the basis of their spectral parameters and that even varieties of a single maceral type can be distinguished. Although the spectra obtained at this time are rather broad and not suitable for chemical structure analysis, the potential for structural analysis exists and may be realized with improvements in instrumentation. 

Alternatively, if better quality data is required only for some small regions of the spectrum, then those regions alone can be scanned to shorten the time needed to obtain an acceptable signal to noise level. The ability to analyze small regions of a coal sample is important even for a single maceral type such as vitrinite. For example, substantial variations occur in the structure (10,11) and swell ability (12) of different microscopic areas of vitrinite from the same coal. 

Our recent development of a new procedure for the density separation of macerals offers a method for obtaining high resolution separation of the three maceral groups exinite, vitrinite, and inertinite, and can further resolve individual maceral types within these macerals groups, e.g., sporinite from alginite in the exinite group (1,2). The procedure... 

Electron spin resonance determinations of g-values, linewidths, radical densities and saturation properties have been performed on carbon radicals in samples of coal macerals isolated by density gradient centrifugation techniques. These data are compared with elemental analyses and density measurements. Each maceral type exhibits a different ESR signature" which can be understood in terms of the nature of the starting organic and the extent of coalification. 

There have been a large number of electron spin resonance (ESR) studies of coal and coal products,(1J but a microscopic interpretation of the resulting data has been hampered by the chemical heterogeneity of the coal samples examined. While several surveys of specially selected macerals have appeared, 3), the recent evolution of maceral separation techniques - now allows detailed ESR observations to be made on coals systematically fractionated in which coal rank, maceral type, and maceral density are simultaneously distinguished. The present report surveys the behavior of a variety of ESR properties of carbon radicals in exinite, vitrinite, and inertinite macerals in a variety of coals of different rank. These data... 

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. 

Some 37 samples from 16 coals of the Pennsylvania State University coal data base (PSOC) were examined. Separate density fractions were obtained by isopycnic density gradient centrifugation of small ( 3iim) coal particles in an aqueous CsCl density gradient. (4J The individual samples are listed by PSOC numbers, coal description, ASTM designation of coal-rank maceral type, and density in Table I. After separation, the samples... 

ESR observations were conducted at 9.5 GHz, using a Varian E-line ESR spectrometer with variable temperature capabilities from 90K-300K. The g value was determined using a Varian pitch standard with a g-value of 2.00302 + 0.00005. The integrated intensity was also calibrated to a Varian pitch standard. The parameters g, AH u, AH-p and the radical density were determined for each sample. Saturation measurements were made on a selected subset of samples. Low temperature runs at 125 K were made for all inertinite samples, as well as for selected samples of the other maceral types. Little temperature variation in g value, linewidth, or lineshape, was seen in any sample. The integrated intensity varied approximately as 1/T, suggesting Boltzmann polarization of the spins at lower temperatures. 

The various maceral types exhibit distinctly different microwave saturation properties. 

Examination of the Py-MS results may provide some understanding of the variation observed between the different maceral types. A distribution pattern of the type shown in Table III has been determined for a select number of macerals which also have been reacted in the pyridine-iodine mixture. In examining the three different possible cases for activation of coal maceral benzylic groups, [1] and possibly [3] would appear to be the most important. From the Py-MS results alkyl pyridines have been found to be much less abundant than alkyl phenols which is not surprising considering the percentage of oxygen compared to... 

Maceral Group Maceral Suite Maceral Type Reflectance under Oil (%) Macerals ... 

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